Showing papers on "Resolution (electron density) published in 1975"
TL;DR: A 7-Å resolution map of the purple membrane has been obtained by electron microscopy of tilted, unstained specimens and shows that Lipid bilayer regions fill the spaces between the protein molecules.
Abstract: A 7-A resolution map of the purple membrane has been obtained by electron microscopy of tilted, unstained specimens. The protein in the membrane contains seven, closely packed, alpha-helical segments which extend roughly perpendicular to the plane of the membrane for most of its width. Lipid bilayer regions fill the spaces between the protein molecules.
2,114 citations
TL;DR: The projected structures of two unstained periodic biological specimens, the purple membrane and catalase, have been determined by electron microscopy to resolutions of 7 A and 9 A, respectively.
1,045 citations
TL;DR: In this paper, a new approach to the study of structure in solids and liquids by pulsed NMR is described, where either multiple-pulse line-narrowing sequences or single pulses, together with an applied linear magnetic field gradient are used.
Abstract: A new approach to the study of structure in solids and liquids by pulsed NMR is described. Either multiple-pulse line-narrowing sequences or single pulses, together with an applied linear magnetic field gradient are used. The theoretical analysis highlights the analogy with plane-wave scattering in optics and is illustrated experimentally with examples of diffraction by ordered and disordered systems and image formation or microscopy. The factors affecting the resolution of the technique are discussed, and the problems of reconstructing micrographs from their projections considered.
250 citations
107 citations
TL;DR: A 6-A resolution structure based on the neutron scattering density profile is proposed for the bilayer, consistent with the electron density profile from x-ray diffraction.
Abstract: Lamellar neutron diffraction from oriented multilayers of hydrated dipalmitoyl lecithin was phased by isomorphous H2O-D2O exchange and swelling techniques. Bound water sites were located in the polar head group region of the bilayer profile. A 6-A resolution structure based on the neutron scattering density profile is proposed for the bilayer. It is consistent with the electron density profile from x-ray diffraction.
101 citations
TL;DR: This paper has first investigated the theory pertaining to the attainable resolution as a function of the electron exposure, the magnification, and several other relevant parameters, and reports experimental results obtained with a commercial image intensifier and with nuclear track photographic emulsion, both of which are highly sensitive recording devices.
99 citations
TL;DR: In this paper, a simple geometrical method for improving the depth resolution of the RBS technique is presented, where a critical appraisal of the resolution-limiting factors such as beam collimation, detector acceptance angle, multiple scattering, and surface topography effects is given in an attempt to optimize the geometry for maximum attainable depth resolution.
96 citations
86 citations
TL;DR: The structure of a new crystal form of deoxyhemoglobin A grown from polyethylene glycol solutions has been determined at 3·5 A resolution and showed minor structural differences near intermolecular contacts, the heme groups, and the β 1 carboxyl terminus.
83 citations
TL;DR: A 3D reconstruction from electron micrographs of tomato bushy stunt virus has been used to determine X-ray phases to 28 A resolution, by analogy with the single isomorphous replacement method of protein crystallography as mentioned in this paper.
82 citations
TL;DR: In this paper, the procedure for computing the resolution function of triple-axis spectrometers is reformulated to make allowance for the spatial configuration of the experimental set-up and for the curvature of the monochromator and analyser crystals.
Abstract: The procedure for computing the resolution function of triple-axis spectrometers is reformulated to make allowance for the spatial configuration of the experimental set-up and for the curvature of the monochromator and analyser crystals. Simple formulae are given for computing the resolution function of conventional instruments as well as of spectrometers with focusing crystals.
TL;DR: In this article, the feasibility of using synchrotron radiation for X-ray diffraction topography has been investigated, and the authors showed that the instrumentation required is far simpler for synchoretron radiation than for conventional sources.
Abstract: With almost perfect silicon crystals and cleaved lithium fluoride crystals as extreme examples, the feasibility of using synchrotron radiation for X-ray diffraction topography has been investigated. In both spatial resolution and strain resolution the synchrotron source diffraction topographs are competitive with topographs obtained using conventional X-ray sources but exposure times are reduced from several hours per cm2 to one second per cm2 using standard recording techniques with Ilford nuclear emulsions. Contrary to (the author's) expectations, the instrumentation required is far simpler for synchrotron radiation than for conventional sources.
TL;DR: The electron density distribution of tobacco mosaic virus has been determined by analysis of the X-ray diffraction pattern given by oriented gels of the virus by separation of overlapping Bessel function terms by a technique analogous to crystallographic isomorphous replacement.
Abstract: The electron density distribution of tobacco mosaic virus has been determined to 6.7 A resolution by analysis of the X-ray diffraction pattern given by oriented gels of the virus. This has been achieved by separation of overlapping Bessel function terms by a technique analogous to crystallographic isomorphous replacement. The course of the polypeptide chain of the coat protein may be traced for a large part of its length.
TL;DR: The construction and the performance of a double-beam Michelson-type Fourier spectrometer are described and the pure rotational spectra of H(2)O and CO have been recorded.
Abstract: The construction and the performance of a double-beam Michelson-type Fourier spectrometer are described. The instrument covers a wavenumber range from 10 cm−1 to 450 cm−1 with a maximum resolution of 0.025 cm−1 and an accuracy of frequency within ±0.001 cm−1. The optical path difference is measured by means of an He–Ne gas laser. To illustrate the general performance of the instrument, the pure rotational spectra of H2O and CO have been recorded.
TL;DR: In this article, the authors applied DTEM to semi-crystalline polymers and demonstrated that the technique permits direct observation of the amorphous and crystalline regions in semi-polymers without any special preparation procedure.
Abstract: Defocus imaging by transmission electron microscopy is applied for the first time to semi-crystalline polymers. The imaging of the amorphous and crystalline regions by this technique is due to the different inner potentials of the two regions. Evidence is presented that the technique permits the direct observation of the amorphous and crystalline regions in semi-crystalline polymers without any special preparation procedure such as staining. In comparison with other known methods, the main advantages of the new technique are better resolution and wider applicability.
TL;DR: An analytic theory of plural incoherent scattering is developed which is general with respect to material and beam voltage and applies to all thicknesses normally encountered, and includes thin specimens as well as thick specimens.
TL;DR: In this article, a system employing medium energy electrons (1-15 keV) for scanning microscopy and diffraction intensity measurements has been constructed, which can be cleaned by argon ion sputtering and heated up to 1000°C.
Abstract: A system employing medium energy electrons (1–15 keV) for scanning microscopy and diffraction intensity measurements has been constructed. The specimen is situated in an UHV environment and can be cleaned by argon ion sputtering and heated up to 1000 °C. The resolution is currently about 300 A for scanning images formed when secondary electrons are detected. The use of diffracted beams to form images is shown to provide new types of information regarding the structure and defects of crystal surfaces. Intensities and intensity profiles of diffracted beams can be measured for comparison with theoretical data and structure analysis.
TL;DR: In this article, a high-resolution X-ray emission spectrum of water vapour is reported and the main lines are analyzed in terms of molecular orbital theory, seven satellites are found and discussed.
Abstract: A high resolution X-ray emission spectrum of water vapour is reported and the main lines are analysed in terms of molecular orbital theory. Seven satellites are found and discussed.
TL;DR: In this article, the aero-filled interferogram is apodized to prevent the generation of artifacts in the spectrum (of a similar origin to the sine x side-lobes formed when a non-zero-filled spectrum is computed with a box-ear truncation function).
Abstract: Digitally recorded spectra containing lines of width less than or equal to the resolution at which the measurement has been made are observed to show some photometric error. In spectra measured by Fourier transform spectroscopy, this error may be substantially reduced if the interferogram is aero-filled. To prevent the generation of artifacts in the spectrum (of a similar origin to the sine x side-lobes formed when a non-zero-filled spectrum is computed with a box-ear truncation function), the aero-filled interferogram must be suitably apodized.
TL;DR: In this article, a mechanism for the dissipation of the point defects is discussed in terms of the reduction and oxidation of the nonstoichiometric crystals of Nb12O29.
Abstract: The reduction of crystals of Nb12O29, having an excess of oxygen, has been studied by high-resolution electron microscopy and electron diffraction. A superstructure and faulted slabs are formed, by aggregation of the point defects forming chains with a limited length in the matrix structure, induced by electron-beam irradiation. Ordering of the chains of point defects in the crystals is directly observed by electron microscopy with resolution of the atomic level. A mechanism for the dissipation of the point defects is discussed in terms of the reduction and oxidation of the nonstoichiometric crystals of Nb12O29.
TL;DR: Calculations show that there is no difference in edge resolution at 100 keV to be expected, in agreement with experiment, and the influence of beam broadening increases relative to the chromatic error with increasing energy.
TL;DR: In this article, the molecular replacement technique in real space (successive cycles of electron density calculations, averaging among non-crystallographically equivalent subunits, and structure factor calculations based upon the improved averaged density) was applied to glyceraldehyde-3-phosphate dehydrogenase.
Abstract: The molecular replacement technique in real space (successive cycles of electron density calculations, averaging among non-crystallographically equivalent subunits, and structure factor calculations based upon the improved averaged density) was applied to glyceraldehyde-3-phosphate dehydrogenase. It was shown possible (i) to extend the phases from a known 6.0 A single isomorphous replacement set to at least 4.9 A resolution; (ii) to determine a reasonable structure at low resolution given the molecular envelope and non-crystallographic symmetry; and (iii) to use the resulting low-resolution phases in the determination of heavy-atom sites. The application of such procedures to the determination of virus structures and heavy-atom derivative sites is discussed.
TL;DR: In this paper, a high resolution electron spectrometer comprising an electron gun, electrostatic lenses, a 127 degrees cylindrical monochromator and analyser, and a collision chamber with rotatable exit slit is presented.
Abstract: The description of a high resolution electron spectrometer comprising an electron gun, electrostatic lenses, a 127 degrees cylindrical monochromator and analyser, and a collision chamber with rotatable exit slit, is presented. Its performance is illustrated by a neon energy loss spectrum and transmission measurements of helium and neon resonances. An analysis of these resonances is also carried out, and values of their energy widths ( Gamma ) and phase shifts ( delta l) are determined.
TL;DR: Experiments on the preparation of thin film sections of embedded protein crystals for investigation by electron microscopy and electron diffraction found that the best resolution observed in diffraction experiments was approximately 10 to 11 A.
TL;DR: In this article, the tensors of the probability moments of the parameters controlled in the measuring device are used in the computation of the resolution function and the application to neutron spectrometry is discussed.
Abstract: Starting from a general definition of the resolution function one gets a rigorous method of calculating the shape of this function. The tensors of the probability moments of the parameters controlled in the measuring device are used in the computation. The application to neutron spectrometry is discussed.
TL;DR: In this article, the model for spot behavior in programmed multiple development (PMD) during solvent advance can predict the number of developments necessary for maximum resolution in Mode 3, and it suggests that any two spots may be completely resolved on a conventional thin-layer chromatography plate by PMD if the ratio R F values is greater than or equal to 1.06.