Showing papers on "Resolution (electron density) published in 1973"
312 citations
219 citations
TL;DR: Rubredoxin from Clostridium pasteurianum was solved at 3 ~ resolution with phases based on a single HgI4 zderivative, for which both reflections of each Friedel pair were measured as discussed by the authors.
Abstract: Rubredoxin from Clostridium pasteurianum is an iron sulfur protein of molecular weight ~ 6100. Crystals are grown by salting out from aqueous (NH4)2804 at pH 4. They belong to the trigonal system, space group R3, hexagonal unit-cell parameters a= b = 64.45, c= 32.68 ~. The structure was solved at 3 ~ resolution with phases based on a single HgI4 zderivative. For the 2 A resolution electron density map, phases were based on two derivatives, HgI4 zand UOI +, for which both reflections of each Friedel pair were measured. From this map a tentative sequence was determined and coordinates for 401 atoms in the molecule were tabulated. The model for the structure has been refined in the usual crystallographic sense beginning at a conventional R of 0.372. Four refinement cycles by AF syntheses and four by least-squares have reduced R to 0.126 for the 5005 reflections with 20\" < I and 0.05 < sin 0/2 < 0.325. Important features of the structure which were uncertain or not evident in the 2 A resolution map have been revealed.
189 citations
TL;DR: In this article, the water vapour spectrum recorded with a resolution of 5 × 10-3 cm-1 between 2930 cm 1 and 4255 cm 1 on a Fourier transform spectrometer is presented.
Abstract: The water vapour spectrum recorded with a resolution of 5 × 10-3 cm-1 between 2930 cm-1 and 4255 cm-1 on a Fourier transform spectrometer is presented. Wavenumbers, attributions and equivalent widths of about 1500 lines are given. Lines of the 2v 2, v 1 and v 3 bands of H2 16O, lines of the hot band v 2 + v 3 - v 2 of H2 16O and lines of the v 1 and v 3 bands of H2 18O and H2 17O are observed.
116 citations
TL;DR: The electron density at 4.5 A resolution of the Fab' fragment of McPC603 mouse myeloma immunoglobulin with phosphorylcholine-binding activity can be divided into four distinct globular regions which are interpreted to correspond to the four domains in the molecule.
Abstract: The electron density at 4.5 A resolution of the Fab' fragment of McPC603 mouse myeloma immunoglobulin with phosphorylcholine-binding activity can be divided into four distinct globular regions which are interpreted to correspond to the four domains in the molecule. The hapten-binding site was located by difference Fourier techniques and lies between two domains near one end of the molecule.
108 citations
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TL;DR: In this paper, a low-loss image from a solid specimen in the high-field region of the condenser-objective lens in a high-resolution SEM was obtained, which demonstrated an edge sharpness of 15 A and a point-to-point resolution of better than 50 A between gold dots on a latex ball on a solid substrate.
Abstract: We have obtained a low‐loss image from a solid specimen in the high‐field region of the condenser‐objective lens in a high‐resolution SEM. These experiments have demonstrated an edge sharpness of 15 A and a point‐to‐point resolution of better than 50 A between gold dots on a latex ball on a solid substrate. In theory, it should be possible to obtain micrographs from solid specimens with a resolution of 10 A by this method.
57 citations
54 citations
TL;DR: In this article, the authors suggest that a recent method of stellar interferometry developed by Labeyrie and his colleagues may be used to obtain diffraction-limited resolution from telescopes whose aberrations are poor by conventional standards.
TL;DR: An electron density map of yeast hexokinase has been calculated at 6 A resolution using six heavy atom derivatives, which shows each of the enzyme's two 51,000 molecular weight subunits to consist of two separate lobes connected by a narrow bridge of density.
TL;DR: In this article, an argon ion laser was used to obtain vibration-rotation spectra of three perpendicular Raman bands of cyclopropane, at a resolution of ca. 0.2 cm−1.
TL;DR: In this article, negative stain microscopy has been used to enhance the visibility of structures of biological interest, such as protein macromolecules, for the purpose of microscopy, which is the production of images of sufficient magnification and resolution that relevant details of the object examined are revealed.
Abstract: Publisher Summary The purpose of microscopy is the production of images of sufficient magnification and of such quality and resolution that relevant details of the object examined are revealed. In recent years, the development of negative stain microscopy has permitted, at least in part, the achievement of that end with respect to protein macromolecules. The electrons of moderate energies satisfy the wavelength requirement as radiation suitable for the study of matter at the atomic and molecular levels. For the study of protein macromolecules, the negative stain technique offers several advantages over other techniques that have been used to enhance the visibility of structures of biological interest. When a specimen is imaged, the variations of electron intensity, or contrast, are produced at the image plane in proportion to the mass distribution, or structure, in the specimen plane. Under the conditions of observation usually established, the minimum thickness of unstained protein, which will result in noticeable contrast, is of the order of 100A. With this limit of resolution, features of large complex structures, which are of the greatest interest, will be lost and smaller protein molecules will be invisible.
TL;DR: In this paper, the responses of dipole-dipole, pole-dipsole, and gradient arrays to a set of ten structures have been computed using the finite element method.
Abstract: The responses of dipole‐dipole, pole‐dipole, and gradient arrays to a set of ten structures have been computed using the finite element method. Comparison of the responses indicates that: (1) The dipole‐dipole array usually gives the largest anomalies, but the anomalies rarely give information on dip of a structure and are strongly influenced by overburden irregularities. This array gives best overall resolution. (2) Pole‐dipole anomalies are almost as large as dipole‐dipole ones and have the same general form but show less resolution. The lower resolution and the asymmetry of this array make results more difficult to interpret. (3) The gradient array provides dip information and good horizontal resolution. Responses to thin vertical structures are weak, anomalies are strongly affected by overburden irregularities, and there is no effective depth discrimination.
TL;DR: In this paper, a system of sodium on a nickel (100) surface is described; resolution is investigated and found to be about +or-0.1 AA, while the top layer of a clean nickel surface is shown to be dilated by not more than 0.15 AA and the determination of the sodium nickel distance of 2.9 AA reported earlier by Andersson and Pendry is described in greater detail.
Abstract: The authors are concerned with extraction of structural information from LEED intensity measurements by comparison with dynamical calculations for trial structures. The technique is illustrated by the system of sodium on a nickel (100) surface. Experiments are described; resolution is investigated and found to be about +or-0.1 AA. The top layer of a clean nickel (100) surface is shown to be dilated by not more than 0.15 AA and the determination of the sodium nickel distance of 2.9 AA reported earlier by Andersson and Pendry is described in greater detail.
TL;DR: In this paper, the small signal gain on the 9 and 10μ bands of CO2 was measured in a portion of an amplifier during and after the passage of a saturating pulse.
Abstract: The small‐signal gain on the 9‐ and 10‐μ bands of CO2 is monitored in a portion of an amplifier during and after the passage of a saturating pulse. The 10°0–02°0 relaxation rate is inferred from this experiment, and a resolution of conflicting previous measurements of this and other rates is offered.
TL;DR: In this paper, the authors derived simple expressions for the form of the intensity distributions in high-resolution dark-field electron micrographs of thin specimens for which the phase-object approximation may be applied.
Abstract: Simple expressions are derived for the form of the intensity distributions in high-resolution dark-field electron micrographs of thin specimens for which the phase-object approximation may be applied. For cases in which the phase change of the electron wave can be assumed to be small it is shown that there is an optimum defocus value which gives the best, interpretable resolution. For dark-field images obtained either with a central beam stop or with a tilted incident beam, the image intensity is shown to depend on the square of the deviation of the projected potential from an average value. The further complications resulting when the phase change cannot be assumed small are discussed and illustrated by means of a simple example.
Journal Article•
TL;DR: In this article, a 2 arc min synthesis study of the spiral galaxy M51 (NGC 5194) has been made in the lambda 21 cm emission line of neutral hydrogen.
Abstract: Abstract : A 2 arc min synthesis study of the spiral galaxy M51 (NGC 5194) has been made in the lambda 21 cm emission line of neutral hydrogen. A morphological HI symmetry axis is found at a position angle of 22 degrees while the dynamically determined major axis is found at a position angle of -8 degrees. The velocities in the north-east outer spiral structure are found to be strongly non-circular. They agree in magnitude with predictions made by Toomre and Toomre for the tidal interaction between M51 and its companion galaxy NGC 5195. A possible continuation in neutral hydrogen of the outermost south-west spiral arm has been detected. M51 also exhibits a strong deficiency in HI surface density at its center. An upper limit of 10 billion solar mass units per beam area has been placed on the neutral hydrogen content of the companion galaxy NGC 5195. This, in turn, yields an upper limit of about 0.1 for the distance-independent ratio M(HI)/L(pg). (Author)
TL;DR: In this paper, the authors described an energy analyzer of the spherical mirror-spherical grid retarding potential type, which obtains high resolution through a small energy overlap between low energy pass and high energy pass filter functions.
Abstract: The energy analyzer described is of the spherical mirror‐spherical grid retarding potential type. It obtains high resolution through a small energy overlap between low energy pass and high energy pass filter functions. The first filter is a spherical electron mirror operating slightly off‐axis in a reflection mode. The second filter is a conventional spherical grid retarding field operating in transmission. Unlike other narrow bandpass monochromators, acceptance angle does not affect resolution and can be made to yield high luminosity. In addition, the resolution varies as the square of the entrance aperture dimension; hence larger entrance aperture areas can be used than for dispersive electron energy analyzers of similar size. This analyzer is examined theoretically, and experimental results as applied to ESCA (electron spectroscopy for chemical analysis) are presented.
TL;DR: X-ray diffraction intensities from frog and cattle retinal rod segments have been interpreted in terms of an electron density distribution along the rod axis and it has been demonstrated that the electron density levels of the asymmetric profile are realistic whereas those of the symmetrical profile are unrealistic.
TL;DR: In this article, it was shown that the boundary regions which are formed by the mottles of the fine structure pattern and which constitute the upper chromosphere are not adequately described by spatial averages, and the properties of the individual structural elements should be taken into account by an appropriate theory, if only in a statistical fashion.
Abstract: Highly resolved Hα spectra and filtergrams obtained at the Fraunhofer Observatory on Capri were analysed by a method whose principles have been described before. As a result the tentative conclusion of our previous work has been confirmed: The mottles of the chromospheric fine structure are clouds superimposed on the low chromosphere. Furthermore, it is proposed that the latter is identical with the interior of the supergranular cells whose spatial averages lend themselves to an interpretation in terms of a spherically symmetric model. On the other hand, we present evidence that the boundary regions which are formed by the mottles of the fine structure pattern and which constitute the upper chromosphere are not adequately described by spatial averages. Instead, the properties of the individual structural elements should be taken into account by an appropriate theory, if only in a statistical fashion. Some of these properties, viz. source function, optical thickness, Doppler width and velocity, were measured for a large number of elements. On the basis of indirect evidence we suggest that the spicules seen on limb photographs of chromospheric lines are identical with the elements of the supergranule boundary structure.
TL;DR: In this paper, a 5145-A argon laser, tuneable over 0.05 A, is used to induce fluorescence in a molecular beam of I2, and the measured width of the individual I2 transitions is 3 MHz, i.e., a resolution of 5×10−9.
Abstract: Laser‐molecular‐beam techniques have been used to observe the hyperfine structure of molecular I2. A 5145‐A argon laser, tuneable over 0.05 A, is used to induce fluorescence in a molecular beam of I2. The measured width of the individual I2 transitions is 3 MHz, i.e., a resolution of 5×10−9. The natural width of the lines has been estimated to be less than 800 kHz.
TL;DR: In the last few years some promising images of biological specimens have been obtained using the high contrast and resolution of dark‐field electron microscopy, however, important problems of image interpretation and difficulties in specimen preparation limit, the usefulness of this mode of image formation is questionable.
Abstract: SUMMARY
In the last few years some promising images of biological specimens have been obtained using the high contrast and resolution of dark-field electron microscopy. However, important problems of image interpretation and difficulties in specimen preparation limit at the present time, the usefulness of this mode of image formation. The destruction of the sample by the electron beam, is of utmost importance. Some possibilities of partly overcoming it are discussed.
TL;DR: In this paper, the 12 0 1-00 and 2 0 1 -00 transitions of CS 2 have been measured with a resolution of 0.25 cm −1 and a consistent set of band constants is given for all the above vibrational transitions.
TL;DR: This investigation has developed strip models for fibrillar axial structure based on reported electron micrographic descriptions of how stainable bands and molecular overlap zones ("backgrounds") are located along the fibrils that are reasonably capable of accounting theoretically for the observed diffraction amplitudes.
TL;DR: In this paper, the characteristics features of a neutron time-of-flight diffractometer, having a resolution Δd / d ∼ 2 × 10 −3 for powder and single crystal diffraction, are described and some first results are presented.