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  • 1
    Electronic Resource
    Electronic Resource
    Structure of acidic haloaluminate melts: Neutron diffraction and quantum chemical calculations (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2733-2741 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of molten mixtures of (KX)y(AlX3)1−y was investigated by neutron diffraction for X=Cl and Br and y=0.25 and 0.33. These melts, known as acidic haloaluminates, contain different ionic species such as AlX−4,Al2X−7, Al3X−10. The diffraction patterns were similar, although not identical, for the same halide pairs and showed features indicative of short-range and intermediate-range order. Quantum chemical calculations were carried out on AlX−4, Al2X−7, and Al3X−10 to provide information needed to interpret the structural results within the framework of the random packing of structural units model. It is shown that the bent Al–X–Al bridge for Al2X−7, obtained from the quantum chemical calculations, is necessary to represent well the structure, and that the values of the bond angles at the central halide atoms are around 110°. Aluminum atoms are found to be tetrahedrally coordinated by the halide atoms, and information on the orientational correlations of neighboring Al2X−7 is derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463063
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  • 2
    Electronic Resource
    Electronic Resource
    Application of new synchrotron powder diffraction techniques to anomalous scattering from glasses : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1308-1310 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have applied two synchrotron powder diffraction techniques to the measurement of high quality anomalous scattering diffraction data for amorphous materials. One of these methods, which uses a curved perfect crystal analyzer to simultaneously diffract multiple powder lines into a position sensitive detector has been shown to possess high resolution, low background, and very high counting rates. This data measurement technique provides excellent energy resolution while minimizing systematic errors resulting from detector nonlinearity. Anomalous scattering data for a Cesium Germanate glass collected using this technique will be presented. The second powder diffraction technique uses a flat analyzer crystal to deflect multiple diffraction lines out of the equatorial plane. Calculations show that this method possesses sufficient energy resolution for anomalous scattering experiments when a perfect crystal analyzer is used and is experimentally much simpler. Future studies will make use of a rapid sample changer allowing the scattering from the sample and a standard material (a material not containing the anomalous scatterer) to be measured alternately at each angle, reducing systematic errors due to beam instability or sample misalignment. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145960
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  • 3
    Electronic Resource
    Electronic Resource
    Pattern of interspecific tiller defoliation in a mixed-grass prairie grazed by cattle (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Grass and forage science 45 (1990), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Permanently marked tillers of five perennial grasses, native to the mixed-grass prairie of North America, were monitored to determine patterns of defoliation, architectural attributes influencing probabilities of defoliation. and post-defoliation responses. Frequency of tiller defoliation was greatest for one of the dominant midgrasses, intermediate for the remaining midgrass and two dominant shortgrasses. and least for the subdominant midgrass. Midgrass species, including the infrequently grazed subordinate species, were consistently grazed more intensively than the shortgrass species. However, the relative intensity of defoliation did not vary among species or grazing periods indicating that intensity of defoliation was primarily a function of pre-defoliation tiller height. Tiller architecture, including height, lamina number and the presence of reproductive culms, did not significantly influence frequency or intensity of defoliation within a species. The lack of evidence supporting tiller architecture as a selection criterion within a species suggests that animals were selecting on vegetation parameters at higher levels of vegetation organization than individual tillers. Grazed tillers of the three midgrasses exhibited greater relative rates of tiller elongation between grazing periods than non-grazed tillers, particularly early in the season when environmental conditions for growth were most favourable. The patterns of interspecific tiller defoliation observed in this study parallel the long-term patterns of grazing-induced species replacement observed in this grassland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2494.1990.tb02201.x
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  • 4
    Electronic Resource
    Electronic Resource
    Levitation apparatus for structural studies of high temperature liquids using synchrotron radiation (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3512-3518 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new levitation apparatus coupled to a synchrotron-derived x-ray source has been developed to study the structure of liquids at temperatures up to 3000 K. The levitation apparatus employs conical nozzle levitation using aerodynamic forces to stably position solid and liquid specimens at high temperatures. A 270 W CO2 laser was used to heat the specimens to desired temperatures. Two optical pyrometers were used to record the specimen temperature, heating curves, and cooling curves. Three video cameras and a video recorder were employed to obtain and record specimen views in all three dimensions. The levitation assembly was supported on a three-axis translation stage to facilitate precise positioning of the specimen in the synchrotron radiation beam. The levitation system was enclosed in a vacuum chamber with Be windows, connections for vacuum and gas flow, ports for pyrometry, video, and pressure measurements. The vacuum system included automatic pressure control and multi-channel gas flow control. A phosphor screen coupled to a high-resolution video microscope provided images of the x-ray beam and specimen shadow which were used to establish the specimen position. The levitation apparatus was integrated with x-ray diffractometers located at X-6B and X-25 beamlines at the National Synchrotron Light Source. X-ray structural measurements have been obtained on a number of materials including Al2O 3, Ni, Si, Ge, and other metallic and ceramic materials in the liquid state. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148315
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  • 5
    Electronic Resource
    Electronic Resource
    Neutron scattering study of H2 adsorption in single-walled carbon nanotubes (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3684-3686 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: H2 adsorption in single-walled carbon nanotubes (SWCNTs) has been studied with quasielastic and inelastic neutron scattering. At 80 K, under a H2 pressure of 110 atm, H2 molecules gradually condense in the SWCNT sample. After pumping out at 25 K and 20 mTorr, the remaining H2 molecules show a quantum rotational transition at 14.5±0.1 meV, with a peak width that increases linearly with increasing temperature from 4.2 to 35 K. The H2 molecules remain in the sample up to 65 K and then start to desorb with increasing temperature. A broad inelastic scattering spectrum from the adsorbed hydrogen is also observed. The time scale of the dynamics is longer than 15 ps even at 200 K. Our results imply that hydrogen molecules are physisorbed in the interstitial tunnels of the SWCNT bundles. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1421639
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of phase separation on short- and intermediate-range order in high-silica Li2O–SiO2 glasses (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 9647-9652 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Wide-angle neutron diffraction measurements have been performed on single-phase and phase-separated high-silica glasses in the system Li2O–SiO2. The structure factors of the single-phase glasses vary modestly with increasing Li2O concentration compared to the changes observed when Na2O or K2O is added to SiO2, and vestiges of the intermediate-range order characteristic of v-SiO2 are retained to 33 mol % Li2O. The structure factors of single-phase and phase-separated glasses are identical to within 1%–2%, indicating that phase separation results in very minor disruptions to local atomic arrangements. When combined with evidence obtained from previous studies, these data indicate that single-phase high-silica glasses in this system contain compositional heterogeneities analogous to those produced by phase separation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468783
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  • 7
    Electronic Resource
    Electronic Resource
    Structure of liquid equiatomic potassium–lead alloy: A neutron diffraction experiment (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2278-2281 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Neutron diffraction measurements have been performed on liquid equiatomic potassium–lead alloy at T=870, 900, and 930 K to determine the influence of temperature on the structure. A well-defined first sharp diffraction peak (FSDP) at Q=0.96 A(ring)−1, similar to that found in glassy materials, was obtained in the total structure factors S(Q) at the three temperatures. While the position of the peak remained unaffected by temperature changes, its magnitude decreased with increasing temperature. The other features of S(Q) were almost unaltered by temperature, as expected. The FSDP can be related to the presence of chemical bonds or clusters whose stability decreases with increasing temperature. A molecular model based on the random packing of K4Pb4 structural units is shown to give a remarkable correspondence with the measured structure factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453157
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  • 8
    Electronic Resource
    Electronic Resource
    New Perspectives on Alzheimer's Disease (1986)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Neuroscience 9 (1986), S. 489-512 
    Details
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ne.09.030186.002421
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  • 9
    Electronic Resource
    Electronic Resource
    Alzheimer's Disease (1985)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Medicine 36 (1985), S. 349-356 
    Details
    ISSN: 0066-4219
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.me.36.020185.002025
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  • 10
    Electronic Resource
    Electronic Resource
    CHEMICAL APPLICATIONS OF NEUTRON SCATTERING (1999)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 50 (1999), S. 571-601 
    Details
    ISSN: 0066-426X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Neutron scattering represents a versatile technique for chemists, as it explores the structure and dynamics of materials at the atomic scale. This review gives an outline of the neutron scattering formalism and describes diffraction and inelastic and quasielastic scattering techniques. Applications to chemistry are illustrated by examples from recent work on crystalline and liquid organic materials, including heterogeneous systems, bulk polymers and polymer solutions. There is particular emphasis on systems where hydrogen bonding plays a significant role. With more powerful sources and improved instrumentation in prospect, there is considerable potential for future extension of these methods to increasingly complex materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physchem.50.1.571
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