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  • Cambridge University Press (CUP)  (6)
  • 1980-1984  (6)
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  • Cambridge University Press (CUP)  (6)
Language
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  • 1980-1984  (6)
Year
  • 1
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 1980
    In:  Proceedings, annual meeting, Electron Microscopy Society of America Vol. 38 ( 1980-08), p. 536-537
    In: Proceedings, annual meeting, Electron Microscopy Society of America, Cambridge University Press (CUP), Vol. 38 ( 1980-08), p. 536-537
    Abstract: Thin, broad crystals of DNA can be grown by slow precipitation in ethanolic aqueous solution (1,2). Crystals of this form are well suited to study by electron diffraction and electron microscopy. In preliminary experiments to test the feasibility of applying electron crystal 1ographic techniques to obtain a direct structure determination of the DNA in these crystals, we have obtained electron diffraction patterns from the crystals. These patterns are the first diffraction patterns of any kind to be obtained from single crystals of highly polymerized DNA.
    Type of Medium: Online Resource
    ISSN: 0424-8201 , 2690-1315
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1980
    SSG: 11
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  • 2
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 1980
    In:  Proceedings, annual meeting, Electron Microscopy Society of America Vol. 38 ( 1980-08), p. 228-229
    In: Proceedings, annual meeting, Electron Microscopy Society of America, Cambridge University Press (CUP), Vol. 38 ( 1980-08), p. 228-229
    Abstract: All photographic emulsions suffer, to varying degrees, from two flaws - they have a limited ability to record accurately minute details and they add noise to whatever they record. To the electron microscopist attempting to do high resolution work on biological material using low electron exposures, these flaws can be of critical importance. The choice of exposure, magnification and emulsion used will determine the amount of detail recorded and the relative influence of the added noise. These choices thus dictate the transfer of information from the image to the emulsion and limit its retrieval by optical and/or computer processing techniques. How does one make a sensible choice?
    Type of Medium: Online Resource
    ISSN: 0424-8201 , 2690-1315
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1980
    SSG: 11
    Location Call Number Limitation Availability
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  • 3
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 1982
    In:  Proceedings, annual meeting, Electron Microscopy Society of America Vol. 40 ( 1982-08-13), p. 78-79
    In: Proceedings, annual meeting, Electron Microscopy Society of America, Cambridge University Press (CUP), Vol. 40 ( 1982-08-13), p. 78-79
    Abstract: The structural damage of molecules irradiated by electrons is generally considered to occur in two steps. The direct result of inelastic scattering events is the disruption of covalent bonds. Following changes in bond structure, movement of the constituent atoms produces permanent distortions of the molecules. Since at least the second step should show a strong temperature dependence, it was to be expected that cooling a specimen should extend its lifetime in the electron beam. This result has been found in a large number of experiments, but the degree to which cooling the specimen enhances its resistance to radiation damage has been found to vary widely with specimen types.
    Type of Medium: Online Resource
    ISSN: 0424-8201 , 2690-1315
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1982
    SSG: 11
    Location Call Number Limitation Availability
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  • 4
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 1980
    In:  Proceedings, annual meeting, Electron Microscopy Society of America Vol. 38 ( 1980-08), p. 234-235
    In: Proceedings, annual meeting, Electron Microscopy Society of America, Cambridge University Press (CUP), Vol. 38 ( 1980-08), p. 234-235
    Abstract: We have investigated the possibility of using a charge coupled device (CCD) as a direct, electron-sensitive readout device for a CTEM. Two-dimensional imaging CCD's, developed as normal television camera elements, are semiconductor devices in which an image is formed on an array of photo-sensitive sites, causing the accumulation of an electric charge proportional to the incident flux. The video signal is generated by sequentially transferring the charges for each element of a line, in bucket-brigade fashion, to the input of the video amplifier. Sensitivity of the CCD to electrons has been demonstrated by the successful application in photocathode tubes, where the photoelectrons are accelerated to an energy up to 15 keV onto the image sensing area of the CCD. The application of the device in a 100 keV transmission electron microscope (Ferrier and Chapman, private communication), with the device in vacuo at the image plane, seems to have promising possibilities for image intensifier, electron counting, and computer input devices. A CCD readout system should have several advantages over previously designed video readout systems, including elimination of the phosphor, fiber optic or lens coupling, and intermediate image intensifier stages. The high gain and low noise of the device should allow detection of single electrons with a detective quantum efficiency near unity.
    Type of Medium: Online Resource
    ISSN: 0424-8201 , 2690-1315
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1980
    SSG: 11
    Location Call Number Limitation Availability
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  • 5
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 1983
    In:  Proceedings, annual meeting, Electron Microscopy Society of America Vol. 41 ( 1983-08), p. 434-435
    In: Proceedings, annual meeting, Electron Microscopy Society of America, Cambridge University Press (CUP), Vol. 41 ( 1983-08), p. 434-435
    Abstract: For many years after the elucidation of the double-helical nature of DNA structure, DNA was thought to exist only in either the A or B conformation. More recently, a great deal of variability in DNA structure has been recognized. Such factors as salt type and concentration, level of hydration, and base sequence have been found to alter the conformation from the original models in both subtle and dramatic ways. The A and B conformations are now seen as families which comprise nearly continuous variations of helical parameters. While structural studies have been carried out on DNA under a fairly wide range of conditions, by both fiber and single crystal x ray diffraction, it is likely that only a small number of the possible conformations of DNA have yet been probed. I have been studying the structure that DNA adopts under conditions which have not been well characterized previously by diffraction experiments, and have found evidence for a DNA conformation which has not previously been described.
    Type of Medium: Online Resource
    ISSN: 0424-8201 , 2690-1315
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1983
    SSG: 11
    Location Call Number Limitation Availability
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  • 6
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 1981
    In:  Proceedings, annual meeting, Electron Microscopy Society of America Vol. 39 ( 1981-08), p. 32-33
    In: Proceedings, annual meeting, Electron Microscopy Society of America, Cambridge University Press (CUP), Vol. 39 ( 1981-08), p. 32-33
    Abstract: The retrieval of high-resolution information from images of biological crystals depends, in part, on the use of the correct photographic emulsion. We have been investigating the information transfer properties of twelve emulsions with a view toward 1) characterizing the emulsions by a few, measurable quantities, and 2) identifying the “best” emulsion of those we have studied for use in any given experimental situation. Because our interests lie in the examination of crystalline specimens, we've chosen to evaluate an emulsion's signal-to-noise ratio (SNR) as a function of spatial frequency and use this as our critereon for determining the best emulsion. The signal-to-noise ratio in frequency space depends on several factors. First, the signal depends on the speed of the emulsion and its modulation transfer function (MTF). By procedures outlined in, MTF's have been found for all the emulsions tested and can be fit by an analytic expression 1/(1+(S/S 0 ) 2 ). Figure 1 shows the experimental data and fitted curve for an emulsion with a better than average MTF. A single parameter, the spatial frequency at which the transfer falls to 50% (S 0 ), characterizes this curve.
    Type of Medium: Online Resource
    ISSN: 0424-8201 , 2690-1315
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1981
    SSG: 11
    Location Call Number Limitation Availability
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