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  • 1
    Electronic Resource
    Electronic Resource
    Data collection in protein crystallography: capillary effects and background corrections (1974)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 30 (1974), S. 740-748 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In protein crystallography, observed diffraction intensities must be corrected for background radiation due to scatter from air and scatter and absorption by capillary., crystal and mother liquor. A systematic study shows that a major contribution to background intensity is air scatter arising from the air intercepted by the direct X-ray beam as 'seen' by the receiving-counter aperture. As a result there is a first-order dependence of background on the 20 angle. The second-order variations in this function are principally due to absorption of the direct beam or air-scattered radiation by the capillary and to diffraction by the glass in the direct beam. To reduce data collection time and crystal exposure, individual background measurements may be approximated by interpolation from empirical background curves or, alternatively, by collecting background intensities for short times and fitting these data with a multidimensional function. If isotropic interpolation is used, i.e., if background is considered to be a function of 2θ alone, systematic errors of up to about 30% can be introduced into the interpolated backgrounds. Methods of accounting for the anisotropy in the background are derived and shown to reduce this error to I-2%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739474001811
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  • 2
    Electronic Resource
    Electronic Resource
    Error analysis in the biophysical applications of a flatbed autodensitometer (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 500-508 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The positional, electronic, and density accuracy of the Syntex AD-1 flatbed autodensitometer is discussed. The standard deviation of optical density measurements due to electronic noise is ± 0.001 optical density units at an optical density of 0, rising to ± 0.04 at an optical density of 2. No deviation from linearity in optical density measurements could be measured. During scanning, the standard deviation in position is less than 1.5 μm. Film grain noise for various films is compared and the effect of signal averaging on this noise is studied. This scanner is compared with other scanners available for accuracy of data collection from precession films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739477001247
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  • 3
    Electronic Resource
    Electronic Resource
    α-Bungaratoxin structure revealed by a rapid method for averaging electron density of non-crystallographically translationally related molecules (1982)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 38 (1982), S. 186-194 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In macromolecular crystallography multiple and independent images of the same chemical species are often present in the crystallographic asymmetric unit. Averaging of density for non-crystallographically related molecules is a powerful technique both for improvement of the density image, and for subsequent phase refinement. Surprisingly often, a non-crystallographic axis of symmetry lies parallel to a crystallographic axis. In such cases, the averaged electron density map can be computed simply and directly from the observed structure factors without subsequent interpolation or averaging in the molecular density map. The procedure described is much more efficient than averaging with consequent interpolation in the real-space domain. The same algorithm can be used in reverse both for very rapid computation of the Fourier transform Fc(s) of a unit cell based on replacement of the 'averaged' density image for the non-crystallographically related molecules, and consequently for a rapid translation function search based on minimization of R = Σ ||Fo| - |Fc|| / Σ |Fo| directly. This residual is much more sensitive than any 'Patterson' search technique where there is overlap between inter- and intramolecular vectors. Jointly these rapid analytic techniques for density averaging and subsequent computation of calculated structure factors from the averaged density map were used to solve and refine the crystal structure of α-bungarotoxin. The rapid translation search and averaging procedures were crucial to the solution of the α-bungarotoxin structure which is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739482000436
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  • 4
    Electronic Resource
    Electronic Resource
    Data collection in protein crystallography: experimental methods for reducing background radiation (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 653-656 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The primary source of background intensity when diffraction intensities are measured by diffractometry is air scatter from the volume of air irradiated by the direct X-ray beam which scatters incident radiation into the photon-detection system. In protein crystallography where crystals are generally enclosed in glass capillaries, scattering of the direct beam from the glass is the second most significant source of background intensity. Glass scattering leads to a broad diffuse ring centered at spacings of 3.0 Å (2θ = 20-32°), whereas air scattering continuously diminishes in intensity between 2θ = 0° and 45° [Krieger, Chambers, Christoph, Stroud & Trus, (1974), Acta Cryst. A30, 740-748]. Compared to these sources of background radiation, other sources are usually insignificant. Two experimental methods are described which reduce the air-scattered component of backgrounds by as much as a factor of 100. Use of these methods increased the peak-to-background ratio by a factor of three-ten times in the case of typical diffractometry of protein crystals. This can be translated into time saving during data collection, and into an increase in the range of measurable intensities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476001356
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  • 5
    Electronic Resource
    Electronic Resource
    The Molecular Neurobiology of the Acetylcholine Receptor (1986)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Neuroscience 9 (1986), S. 383-413 
    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.09.030186.002123
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  • 6
    Electronic Resource
    Electronic Resource
    Mechanisms of Zymogen Activation (1977)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Biophysics and Biomolecular Structure 6 (1977), S. 177-193 
    Details
    ISSN: 0084-6589
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.bb.06.060177.001141
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  • 7
    Electronic Resource
    Electronic Resource
    Suppression of superconductivity by injection of spin-polarized current : 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. 6774-6776 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A spin polarized current has been injected into high Tc superconductors resulting in a significant reduction in the superconductor's critical current. Such injection may serve as the basis of a new class of superconducting devices for control, switching and amplification. Preliminary results using both Permalloy and CMR materials as injectors are presented. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367763
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  • 8
    Electronic Resource
    Electronic Resource
    Laser-based processing of polymer nanocomposites for chemical sensing applications (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5739-5746 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pulsed laser deposition (PLD) has been used to fabricate polymer/carbon nanocomposite thin films for use in chemical sensors (chemiresistors). Ethylene vinyl acetate copolymer (EVA) films (undoped and 20% carbon by weight) were deposited using an ArF excimer laser (193 nm) at fluences between 150 and 300 mJ/cm2. The structure and morphology of the deposited films were characterized using Fourier transform infrared spectroscopy (FTIR), Raman scattering, and transmission and scanning electron microscopy (TEM). An analysis of the FTIR spectra indicates that a film deposited using an undoped EVA target is primarily polyethylene, suggesting that the acetate group is photochemically or photothermally removed from the starting material. Gas phase measurements of the laser-evaporated material using a quadrupole time of flight mass spectrometer confirm the production of the acetyl radical on the target surface. Analysis of TEM of films deposited using C-doped targets shows that the carbon black particles (initially 50 nm particles in 1 μm agglomerates) are broken down into particles that are ≤50 nm in the deposited film. Incorporation of carbon into the target reduces the degree of photochemical damage of the starting material, as shown in the FTIR spectra of the deposited film. The sensitivity and response time of chemiresistors fabricated from 6 μm thick composite films on top of gold electrodes were measured using toluene vapor (548 ppm). The chemiresistors exhibited a reversible and fast (〈1.3 s) response to the vapor. In comparison to data reported in the literature, chemiresistors fabricated from PLD films are significantly better than devices fabricated using a more conventional polymer film growth technique. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1362405
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic, structural, and transport properties of thin film and single crystal Co2MnSi (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4396-4398 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic, structural, and transport properties of the Heusler alloy Co2MnSi are reported for sputtered thin films and a single crystal. X-ray diffraction reveals a phase pure L21 structure for all films grown between 573 and 773 K. Films grown at 773 K display a four-fold decrease in the resistivity relative to those grown at lower temperatures and a corresponding 30% increase in the residual resistivity ratio (ρ300 K/ρ5 K). We show that the higher growth temperature results in lattice constants, room temperature resistivities, and magnetic properties that are comparable to that of the bulk single crystal. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1428625
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  • 10
    Electronic Resource
    Electronic Resource
    Stable Ti-based quasicrystal offers prospect for improved hydrogen storage (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2998-3000 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The desorption of hydrogen from a novel material, a Ti45Zr38Ni17-H quasicrystal, was observed using high-temperature powder x-ray diffraction, demonstrating the potential utility of Ti-based quasicrystals in place of crystalline or amorphous hydrides for hydrogen storage applications. The maximum observed change in hydrogen concentration was from 61 at. %, corresponding to a hydrogen-to-metal ratio (H/M) of 1.54, at 91 °C to less than 2.5 at. % (H/M=0.025) at 620 °C. The onset temperature of desorption is below 350 °C. Surface oxidation was found to promote the formation of crystalline hydride phases. Highly oxidized samples transformed to a mixture of the C14 Laves and C15 Laves crystalline hydrides, and the Ti2Ni phase. When the oxidation was less severe, a reversible transformation between the quasicrystal and crystalline hydride phases was clearly observed, demonstrating the stability of the Ti45Zr38Ni17 quasicrystal at very low hydrogen concentrations, and temperatures as high as 661 °C. This is the first evidence for a stable Ti-based quasicrystal and for reversible hydrogen storage in a quasicrystalline phase. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117756
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