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  • 1
    Electronic Resource
    Electronic Resource
    New high temperature furnace for structure refinement by powder diffraction in controlled atmospheres using synchrotron radiation (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3554-3561 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A low thermal gradient furnace design is described which utilizes Debye–Scherrer geometry for performing high temperature x-ray powder diffraction with synchrotron radiation at medium and high energies (35–100 keV). The furnace has a maximum operating temperature of 1800 K with a variety of atmospheres including oxidizing, inert, and reducing. The capability for sample rotation, to ensure powder averaging, has been built into the design without compromising thermal stability or atmosphere control. The ability to perform high-resolution Rietveld refinement on data obtained at high temperatures has been demonstrated, and data collected on standard Al2O3 powder is presented. Time-resolved data on the orthorhombic to rhombohedral solid state phase transformation of SrCO3 is demonstrated using image plates. Rietveld refinable spectra, collected in as little as 8 s, opens the possibility of performing time-resolved structural refinements of phase transformations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149948
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  • 2
    Electronic Resource
    Electronic Resource
    A metallurgical approach toward alloying in rare earth permanent magnet systems (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. 4847-4847 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In bulk permanent magnets, the extrinsic properties relating to the microstructure determined the level of hard magnetic properties that is actually achieved. Many researchers have worked on the microstructure property relationships in the Nd2Fe14B (2-14-1) system but, in general, the approach has been to analyze the microstructure of materials which have been shown to have good magnetic properties rather than to study the effect of alloy additions on the metallurgical properties of the system. The microstructure which is obtained under a given set of processing conditions is highly dependent on the solidification behavior of the alloy, as well as grain growth phenomena. Alloy additions which effect the solidification behavior of the melt and then form precipitates which pin grain boundaries, and therefore control grain size, should be valuable in producing the uniform microstructure required for good magnetic properties. A number of refractory metal carbides perform both of these functions. The carbides have a reasonable degree of solubility in the 2-14-1 melt and, under conditions of reasonable rapid solidification, a degree of metastable solubility in the 2-14-1 phase. However, there is very limited equilibrium solid solubility in the 2-14-1 phase so that the intrinsic magnetic properties are not effected. The addition of these materials to 2-14-1 results in a factor or three reduction of the quench rate required to produce amorphous material. In addition, the crystallization temperature of the glass is enhanced leading to enhance nucleation and finer grain size during crystallization. Finally refractory metal carbide precipitates decorate the grain boundaries of the crystallized material inhibiting grain growth. Transition metal carbide formation, solid and liquid solubility, effects on solidification, nucleation, and grain growth will be discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361629
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of TiC additions to the microstructure and magnetic properties of Nd9.5Fe84.5B6 melt-spun ribbons : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6631-6633 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rapidly solidified samples of Nd9.5Fe84.5B6 with and without 3 at. % TiC were prepared by melt spinning and melt extraction and then annealed in vacuum (3×10−6 Torr) at temperatures from 600 to 750 °C. For alloys melt spun under similar conditions, the overquenched state was achieved at wheel speeds 〉10 m/s for the TiC added alloy while 〉20 m/s was necessary without TiC. The overquenched samples contained a smaller fraction of α-Fe in smaller grains than the undercooled samples where Fe dendrites formed near the free surface during solidification. These Fe dendrites were not removed by annealing. In addition, large orientated 2-14-1 grains nucleated on the Fe dendrites. This combination is detrimental to the magnetic properties. The addition of TiC results in improved control of the microstructure over a larger fraction of the ribbon volume enhancing the magnetic properties. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367929
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanism for flux pinning in NdBa2Cu3O7−δ melt-textured in low oxygen partial pressure (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3572-3574 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When NdBa2Cu3O7−δ (Nd123) is melt-textured in low oxygen partial pressure (Po2) and subsequently annealed in oxygen to produce the superconducting phase, there is a considerable enhancement of flux pinning compared to Y123. This enhancement is accompanied by a precipitation mechanism due to a change of the solubility limits of Nd1+xBa2−xCu3O7−δ between the high temperature low Po2 conditions used in melt-textured growth and the low temperature oxygen annealing. Transmission electron microscopy reveals a coherent intermediate precipitate structure with a composition of BaCuO2 and a high density of dislocations. We believe these defects are responsible for the strong flux pinning in this material. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120395
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  • 5
    Electronic Resource
    Electronic Resource
    Growth of nucleation sites on Pb-doped Bi2Sr2Ca1Cu2O8+δ (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 556-558 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the growth of Bi2Sr2Ca2Cu3O10+δ from mixed powders of Pb-doped Bi2Sr2Ca1Cu2O8+δ and other oxides, it has been discovered that a dense array of hillocks or mesas grow at the interface between a Ag overlay and Pb-doped Bi2Sr2Ca1Cu2O8+δ grains during the ramp up to the reaction temperature. As viewed in an environmental scanning electron microscope, the Ag coated grains develop a texture that looks like "chicken pox'' growing on the grains at about 700 °C. These hillocks are about 100 nm across and are spaced at about 500 to 1000 nm. If there is no Ag, this texture does not develop. Preliminary measurements indicate that the hillocks are a recrystallization of (Bi,Pb)2Sr2Ca1Cu2O8+δ, and are definitely not a Pb rich phase. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116398
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  • 6
    Electronic Resource
    Electronic Resource
    A generalized solidification model and microstructural verification for the Nd–Fe–B–Ti–C system processed by rapid solidification : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4459-4461 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the Nd2Fe14B (2-14-1) compound, the optimal grain size should be smaller than the size of the single domain size of 150 nm. Transition metal carbides (TMC) also reduce the quench rate necessary to achieve the optimal or overquenched condition. This allows inert gas atomization (IGA) to produce viable magnetic materials. In this article we will demonstrate that optimal microstructure for the 2-14-1 can be produced by IGA with the addition of TiC. Moreover, a solidification model will be presented to show (1) how recalescence is a critical feature to the evolution of the microstructure in rapidly solidified materials and (2) the role TMC and other solute phases have on inhibiting grain growth so that lower quench rates can be employed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364975
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of a single-strand origin, ssoU, required for broad host range replication of rolling-circle plasmids (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 33 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Single-stranded DNA (ssDNA) promoters are the key components of the single-strand origins (ssos) of replication of rolling-circle (RC) replicating plasmids. The recognition of this origin by the host RNA polymerase and the synthesis of a short primer RNA are critical for initiation of lagging-strand synthesis. This step is thought to be a limiting factor for the establishment of RC plasmids in a broad range of bacteria, because most of the ssos described are fully active only in their natural hosts. A special type of sso, the ssoU, is unique in the sense that it can be efficiently recognized in a number of different Gram-positive hosts. We have experimentally deduced the folded structure and characterized the ssDNA promoter present within the ssoU using P1 nuclease digestion and DNase I protection assays with the Bacillus subtilis and Staphylococcus aureus RNA polymerases. We have also identified the RNA products synthesized from this ssDNA promoter and mapped the initiation points of lagging-strand synthesis in vivo from ssoU-containing plasmids. Through gel mobility shift experiments, we have found that ssDNA containing the ssoU sequence can efficiently interact with the RNA polymerase from two different Gram-positive bacteria, S. aureus and B. subtilis. We have also realigned the narrow and broad host range sso sequences of RC plasmids, and found that they contain significant homology. Our data support the notion that the strength of the RNA polymerase–ssoU interaction may be the critical factor that confers the ability on the ssoU to be fully functional in a broad range of bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01471.x
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  • 8
    Electronic Resource
    Electronic Resource
    Etalon effect in wave-mixing experiments with photorefractive crystals (1998)
    Springer
    Applied physics 67 (1998), S. 583-586 
    Details
    ISSN: 1432-0649
    Keywords: PACS: 42.65.Hw; 42.70.Nq; 42.70.Ln
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: We present investigations of the etalon effect in sillenite photorefractive crystals with a pulsed frequency-doubled Nd:YAG laser and show its influence on two- and four-wave mixing. In four-wave mixing the etalon effect allows changes of the diffraction efficiency by more than 80%. Results are supported by theoretical considerations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003400050550
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  • 9
    Electronic Resource
    Electronic Resource
    Partial melting during formation of YBa2Cu3O7−x (1997)
    Springer
    Journal of materials science 16 (1997), S. 988-990 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Abstracts are not published in this journal
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018537516176
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  • 10
    Electronic Resource
    Electronic Resource
    Function of coated membranes and multivesicular bodies during membrane regulation in stimulated exocrine pancreas cells (1974)
    Springer
    Cell & tissue research 156 (1974), S. 1-20 
    Details
    ISSN: 1432-0878
    Keywords: Exocrine pancreas ; Cell membrane regulation ; Coated vesicles, Multivesicular bodies ; Endocytosis ; Autoradiography, Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Stimulation of secretion by pilocarpine results in a 70% loss of zymogen granules from pancreatic acinar cell during the first hr after injection of the drug. In previous work (Geuze and Poort, 1973), we found that the amount of membrane stored in the surface of the microvilli and of the numerous infoldings present in highly stimulated cells, increases during the first 2 hr and then decreases again during the 3rd hr after stimulation, concurrently with maximal endocytosis of sorbitol-[su14C]. Further observations on the fine structure of stimulated cells at various time intervals after injection of pilocarpine showed that during the first hr numerous smooth vesicles and multivesicular bodies (mvb's) appear in the apical cytoplasm, while the number of coated vesicles and their relative total volume increase significantly 3 hr after stimulation. By infusion of ferritin in the pancreatic duct system in vivo and application of cytochemical techniques (osmium impregnation, electron microscope autoradiography and acid phosphatase cytochemistry) it could be established that after stimulated exocytotic secretion, redundant apical cell membrane is withdrawn by at least two routes: 1) During the initial rapid increase of the amount of apical cell membrane, withdrawal is accomplished by interiorization of luminal invaginations into smooth endocytotic vesicles, which in turn give rise to mvb's by infolding and subsequent fission of their limiting membrane. 2) Once the bulk of stored secretion granules has been discharged, endocytotic coated vesicles become gradually more prominent as carriers for redundant cell membrane. The contents of endocytotic structures ultimately become incorporated in residual bodies, suggesting lysosomal degradation of cell membrane prior to eventual reutilization. Coated vesicles also originate by pinching off from mature Golgi cisternae and condensing vacuoles. A possible function of the coated membranes in the concentration of exportable protein within forming secretory granules is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220098
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