Showing papers on "Resolution (electron density) published in 1971"
TL;DR: Tests of the convolution method with computer-simulated shadowgraphs show that it is also more accurate than the Fourier transform method, and has good potentialities for application in electron microscopy and x-radiography.
Abstract: A new technique is proposed for the mathematical process of reconstruction of a three-dimensional object from its transmission shadowgraphs; it uses convolutions with functions defined in the real space of the object, without using Fourier transforms. The object is rotated about an axis at right angles to the direction of a parallel beam of radiation, and sections of it normal to the axis are reconstructed from data obtained by scanning the corresponding linear strips in the shadowgraphs at different angular settings.
Since the formulae in the convolution method involve only summations over one variable at a time, while a two-dimensional reconstruction with the Fourier transform technique requires double summations, the convolution method is much faster (typically by a factor of 30); the relative increase in speed is larger where greater resolution is required. Tests of the convolution method with computer-simulated shadowgraphs show that it is also more accurate than the Fourier transform method. It has good potentialities for application in electron microscopy and x-radiography. A new method of reconstructing helical structures by this technique is also suggested.
967 citations
TL;DR: In this paper, the Fourier transform of the image of a thin crystal of catalase, which has discrete diffraction maxima in the resolution range of 10 to 2.5 nm, as a function of defocusing, was determined by finding the relative contributions from phase and amplitude contrast.
Abstract: The effects of defocusing and spherical aberration in the electron microscope image are most simply and directly displayed in the Fourier transform of the image. We have investigated the process of image formation by determining the changes in the transform of the image of a thin crystal of catalase, which has discrete diffraction maxima in the resolution range of 10 to 2.5 nm, as a function of defocusing. The changes in amplitude and phase of these diffraction maxima have been measured and compared with the predictions of a first-order theory of image formation. The theory is generally confirmed, and the transfer function of the microscope is completely determined by finding the relative contributions from phase and amplitude contrast. A 'true' maximum contrast image of the catalase crystal, compensated for the effects of defocusing, is reconstructed from the set of micrographs in the focal series. The relation of this compensated image to individual underfocused micrographs, and the use of underfocus contrast enhancement in conventional electron microscopy, are discussed. This approach and the experimental methods can be extended to high resolution in order to compensate for spherical aberration as well as defocusing. In as much as spherical aberration is the factor presently limiting the resolution of electron lenses, this could provide a considerable extension of the resolution of the electron microscope.
339 citations
TL;DR: The electron density map has been calculated at 6 A resolution for a human γG1 immunoglobulin molecule and is interpreted in terms of four possible models, of which a T-shaped model is favored.
225 citations
TL;DR: In this article, a computer program based on a procedure discussed by Powell has been developed for the resolution of overlapping peaks in data output from x-ray diffraction, ion-exchange chromatography with spectroscopic detection, and infrared spectroscopy.
Abstract: A computer program based on a procedure discussed by Powell has been developed for the resolution of overlapping peaks in data output from x-ray diffraction, ion-exchange chromatography with spectroscopic detection, and infrared spectroscopy. A polynomial background is also fitted to the data so that recourse to arbitrary graphical methods for separating peaks and background is no longer necessary.
175 citations
127 citations
Journal Article•
TL;DR: A three-dimensional electron density map has been calculated at 6 A resolution for a human γG1 immunoglobulin molecule and the dimensions of this model compare extremely well with those reported by other physical and chemical techniques for immunoglOBulin molecules.
Abstract: A three-dimensional electron density map has been calculated at 6 A resolution for a human γG1 immunoglobulin molecule. X-ray diffraction data have been collected for the native protein crystals and for three heavy atom derivatives prepared by soaking the crystals in PCMBS, Hg(CN)2 and PtCl6-. Three distinct globular regions have been identified in the electron density map. One of these surrounds the molecular dyad axis and has been interpreted to be the Fc fragment. The other two regions are identical to one another and have been interpreted to be the Fab fragments. There are four ways of joining these globular regions of electron density to make a complete molecule and these lead to four possible models of which a T-shaped model is favored. The dimensions of this model compare extremely well with those reported by other physical and chemical techniques for immunoglobulin molecules.
60 citations
TL;DR: In this article, the effects of tip temperature (T T ), imaging gas mixture, and electric field strength on the resolution of the field ion microscope have been measured quantitatively, and it was shown that the image diameter of individual tungsten atoms had a quadratic dependence on T T between 11 °K and 62°K.
57 citations
TL;DR: In this paper, the infrared spectra of gaseous HCF 3 and DCF 3 were recorded with a resolution between 0.2 and 1.0 cm −1, and the contours of the fundamentals were analyzed in part by classical methods and by contour simulation by a computer.
57 citations
TL;DR: From an analysis of the packing in the unit cell it is concluded that the molecular dimensions are approximately 80 by 33 by 28 A, indicating that the double-helical portions of the transfer RNA molecule are approximately half a helical turn in length, and therefore can contain 4-7 base pairs.
Abstract: Yeast phenylalanyl transfer RNA crystallizes in a simple orthorhombic unit cell (a = 33.2, b = 56.1, c = 161 A), and the crystal yields an x-ray diffraction pattern with a resolution of 2.3 A. From an analysis of the packing in the unit cell it is concluded that the molecular dimensions are approximately 80 by 33 by 28 A. The diffraction pattern viewed along the a-axis has a distribution characteristic of double-helical nucleic acids. However, this distribution is not found when the pattern is viewed along the b-axis. This has been interpreted as indicating that the double-helical portions of the transfer RNA molecule are approximately half a helical turn in length, and therefore can contain 4-7 base pairs. These results are consistent with the cloverleaf formulation of transfer RNA secondary structure.
57 citations
TL;DR: It is proved that interesting images cannot be uniquely described by any finite number of projections, and thus any reconstruction technique can only hope to give an approximation to the original.
51 citations
01 Jan 1971
TL;DR: In this article, Bourbaki et al. implique l'accord avec les conditions générales d'utilisation (http://www.numdam.org/legal.php).
Abstract: © Association des collaborateurs de Nicolas Bourbaki, 1970-1971, tous droits réservés. L’accès aux archives du séminaire Bourbaki (http://www.bourbaki. ens.fr/) implique l’accord avec les conditions générales d’utilisation (http://www.numdam.org/legal.php). Toute utilisation commerciale ou impression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright.
TL;DR: In this paper, a high resolution Si(Li) spectrometer system was used to measure the spectra of X-rays and a study of the variation of the photopeak to background ratio as a function of target thickness was carried out for the purpose of estimating the analytical sensitivity of the technique.
TL;DR: Applications of the asymmetric mode to line strength measurements and to determination of partial pressures of absorbing constituents in gas mixtures are discussed.
Abstract: A high resolution interferometer in the Michelson configuration has been designed and constructed for the purpose of studying the optical properties of gases in either the symmetric or asymmetric mode of operation. The performance of this instrument in the 20-220 cm(-1) spectral region is demonstrated by measurements on a few simple molecules. A working resolution of 0.05 cm(-1) is verified by observation of the isotopic splitting in HC1 and by the resolution of several doublets in the H(2)O spectrum. Applications of the asymmetric mode to line strength measurements and to determination of partial pressures of absorbing constituents in gas mixtures are discussed.
TL;DR: In this article, the emission spectrum of RuC obtained in a King furnace has been photographed in a high resolution Eagle spectrograph between 6 000-8 700 A. 46 bands were detected in this region.
Abstract: The emission spectrum of RuC obtained in a King furnace has been photographed in a high resolution Eagle spectrograph between 6 000-8 700 A. 46 bands were detected in this region. From a vibrational analysis it seems most likely that they belong to 8 sub-systems. The final arrangement of these sub-systems into systems has not been successful. For the most intense sub-system with the 0-0 band situated at 7 224 A the following molecular constants in cm-1 were derived:
TL;DR: A scanning microscope is described which is capable of a point resolution of 0.5 nm and can produce the same kinds of micrographs as a conventional microscope, however, by using several detectors to produce signals corresponding to different groups of transmitted electrons it is able to produce an image contrast closely proportional to Z, the atomic number.
Abstract: A scanning microscope is described which is capable of a point resolution of 0.5 nm. We have demonstrated that it can produce the same kinds of micrographs as a conventional microscope. However, by using several detectors to produce signals corresponding to different groups of transmitted electrons we are able to produce an image contrast closely proportional to Z, the atomic number. Such a system is very promising for the study of stained molecules.
TL;DR: In this paper, the use of redundancy principles (similar to X-ray structure determination) is discussed and demonstrated for electron microscopy of organic specimens, especially in the case of radiation damage.
Abstract: Electron microscopy using microscopes with conventional magnetic lenses is restricted in resolution by spherical aberration. The 'zonal correction principle' allows this limit to be overcome. Its use in image reconstruction schemes allows separation of the influence of defocusing, astigmatism, etc., from the physically significant structure. The use of three-dimensional methods of image differencing is necessary in order to get interpretable results in the study of the not 'infinitely thin' objects in electron microscopy at atomic level. The use of redundancy principles (similar to X-ray structure determination) is discussed and demonstrated. The most severe difficulty, especially in electron microscopy of organic specimens, is radiation damage.
TL;DR: A Fourier map of concanavalin A is computed at 2.8 A resolution by the multiple isomorphous replacement technique and the interpretation of that portion of the map which is clearly identifiable as the transition metal-binding site is presented.
TL;DR: In this paper, the photoelectron spectra of H 2 O and D 2 O have been measured with sufficient resolution to partially resolve: rotational structure, and the similarity between the band resulting from the photo-electron transition to the ground ionic state 2 B 1, and one of the molecular Rydberg transitions is discussed.
TL;DR: In this article, a test method is described which will reveal some common distortions in the scanning electron microscope and also a measure of signal-to-noise ratio at the display console.
Abstract: A test method is described which will reveal some common distortions in the scanning electron microscope. The test will give a measure of resolution and also a measure of signal-to-noise ratio at the display console.
TL;DR: In this article, the rotational strengths associated with the p-band transition calculated for the (S)-configuration of 6,6′-disubstituted-bis-1,1′-spiroindanes agree with the positions and signs observed for the compounds derived from (−)-IIIc, establishing the absolute configuration of this series.
Abstract: The resolutions of 6,6′-dihydroxy-3,3,5,3′,3′,5′-hexamethyl-bis-1,1′-spiroindane (IIIa), 3,3,3′,3′-tetramediyl-bis-1,1′-spiroindane-6,6′-dicarboxylic acid (IIIc), and 5,5′-dihydroxy-bis-1,1′-spiroindane (VIII) are reported. The circular dichroism and absorption spectra of these optically active compounds and their derivatives were measured. The spectra were analysed by means of a coupled oscillator model. The relative frequencies and signs of the rotational strengths associated with the p-band transition calculated for the (S)-configuration of 6,6′-disubstituted-bis-1,1′-spiroindanes agree with the positions and signs of the CD bands observed for the compounds derived from (−)-IIIc, establishing the absolute configuration of this series. The result was confirmed by the X-ray diffraction study of (−)-7,7′-dibromo-derivatives prepared from (+)-IIIa. It was found that these spiro compounds having the (S)-configuration showed a negative CD band in the longest wavelength region, except for the case in which th...
TL;DR: In this article, the i.r. spectra of the perpendicular bands v 6 and v 2 + v 6 of CH 3 I have been measured with a resolution of about 0.03 cm −1.
TL;DR: In this article, energy losses of 37 keV electrons in solid Ar, Ne and H 2 were measured with a resolution better than 0.08 eV and compared with optical results.