Showing papers on "Resolution (electron density) published in 1992"
TL;DR: In this article, the authors demonstrate that high resolution in the 13C spectrum can be obtained in an efficient manner by using a "constant-time" 13C evolution period, where the effect of 13C15N J coupling can be removed in a straightforward manner by the use of broadband 15N decoupling.
395 citations
TL;DR: It is shown that the contrast in high-resolution electron micrographs of biological macromolecules, illustrated by a study of TMV in ice, falls considerably below the level which should theoretically be attained, the principal limitation to atomic-resolution structure determination by electron microscopy.
130 citations
TL;DR: In this article, a method is presented for the rapid, objective and automatic comparison of selected parts of protein surfaces as a function of resolution using differences and correlations of Fourier coefficients.
Abstract: Resolution is a crucial parameter to consider in making surface comparisons. A method is presented here for the rapid, objective and automatic comparison of selected parts of protein surfaces as a function of resolution using differences and correlations of Fourier coefficients. A test-case application of this procedure to the surfaces of five immunoglobulin antigen-combining sites allowed them to be partitioned into two categories.
116 citations
TL;DR: It is shown that compensation for the contrast transfer function is necessary and sufficient to convert the images into accurate representations of molecular density and in quantitative agreement with the atomic model derived from X-ray results.
112 citations
TL;DR: O'Keefe and Spence as discussed by the authors reviewed the various definitions of high-resolution transmission electron microscopy (HRTEM) resolution, derived theoretical expressions for resolution, and suggested how high resolutions may be attained in practice.
110 citations
25 Oct 1992
TL;DR: In this paper, the spatial resolution in a reconstructed single photon emission computed tomography (SPECT) image is influenced by the intrinsic resolution of the detector, and the photon-counting efficiency of SPECT systems is also determined by intrinsic resolution.
Abstract: The spatial resolution in a reconstructed single photon emission computed tomography (SPECT) image is influenced by the intrinsic resolution of the detector, and the photon-counting efficiency of SPECT systems is also determined by the intrinsic resolution. The authors demonstrate that improvements in detector resolution can lead to both improved spatial resolution in the image and improved counting efficiency compared to conventional systems. This paradoxical conclusion results from optimizing the geometry of a multiple-pinhole coded-aperture system when detectors of very high resolution are available. Simulation studies that demonstrate the image quality that is attainable with such detectors are reported. Reconstructions are performed using an iterative search algorithm on a custom-designed parallel computer. The imaging system is described by a calculated system matrix relating all voxels in the object space to all pixels on the detector. A resolution close to 2 mm is found on the reconstructed images obtained from these computer simulations with clinically reasonable exposure times. This resolution may be even further improved by optimization of the multiple-pinhole aperture. >
97 citations
94 citations
TL;DR: How the application of cryoelectron microscopy, three-dimensional image reconstruction, and X-ray crystallography provides a power-ful approach to study large, unstable macromolecular complexes is reported.
Abstract: Biological processes frequently require the formation of multi-protein or nucleoprotein complexes. Some of these complexes have been produced in homogeneous form, crystallized, and analysed at high resolution by X-ray crystallography (for example, see refs 1-3). Most, however, are too large or too unstable to crystallize. Individual components of such complexes can often be purified and analysed by crystallography. Here we report how the coordinated application of cryoelectron microscopy, three-dimensional image reconstruction, and X-ray crystallography provides a powerful approach to study large, unstable macromolecular complexes. Three-dimensional reconstructions of native cowpea mosaic virus (CMPV) and a complex of CPMV saturated with a Fab fragment of a monoclonal antibody against the virus have been determined at 23 A resolution from low-irradiation images of unstained, frozen-hydrated samples. Despite the nominal resolution of the complex, the physical footprint of the Fab on the capsid surface and the orientation and position of the Fab have been determined to within a few angstroms by fitting atomic models of CPMV4 and Fab (Kol)5 to reconstructed density maps.
88 citations
TL;DR: Experiments have been performed to evaluate the likely spatial resolution performance of a possible screening for breast cancer using harmless doses of visible or near-infrared radiation, and suggest that a resolution of a few millimeters is achievable with a system with a temporal resolution of about 10 ps.
Abstract: An imaging system is being developed as a possible means of screening for breast cancer using harmless doses of visible or near-infrared radiation. This system produces transmission images of highly scattering objects by recording and discriminating between the times-of-flight of transmitted photons. Experiments have been performed to evaluate the likely spatial resolution performance of such a system. This involved measuring the edge profile produced by an opaque mask embedded in a highly scattering medium, and evaluating the spatial resolution as a function of the period of time over which transmitted light was integrated. The results suggest that a resolution of a few millimeters is achievable with a system with a temporal resolution of about 10 ps.
88 citations
Patent•
31 Jan 1992TL;DR: In this article, a multiple-resolution optically encoded label is presented, which is readable at two or more optical resolutions, and is able to store two-or more respective channels of optically encode information.
Abstract: A multiple resolution optically encoded label is readable at two or more optical resolutions, and is able to store two or more respective channels of optically encode information. Low resolution information is encoded in a plurality of large cells arranged in a predetermined geometric pattern. Each of the large cells includes a plurality of smaller cells for storing high resolution information. Method and apparatus are disclosed for encoding both high resolution data, and low resolution data, as well as for finding and reading both high resolution and low resolution data.
87 citations
TL;DR: In this paper, the physical priciples behind X-ray microscopes, the types of optical systems used and their achievable resolution are discussed, as well as the application of soft X-rays to the imaging of biological, materials science, geological and other specimens.
TL;DR: A correction technique for matching the resolution of all the frequencies of the SSM/I to the 25-km spatial resolution of the 37-GHz channel is described and it is found that the approach produces adequate enhancement of the spatial resolution to make such a correction worthwhile.
Abstract: The authors describe and apply a correction technique for matching the resolution of all the frequencies of the Special Sensor Microwave/Imager (SSM/I) to the 25-km spatial resolution of the 37-GHz channel. To accomplish this, it is necessary to increase the spatial resolution of the 19- and 22-GHz channels while degrading that of the 85-GHz channel. It is found that the approach produces adequate enhancement of the spatial resolution to make such a correction worthwhile. Results suggest that this technique decreases brightness temperature differences stemming solely from spatial resolution differences by over 50% for the low resolution channels with only a modest increase in random noise. The correction can also help to better resolve small features which would otherwise be lost due to the lack of resolution. >
TL;DR: The secondary structure of streptokinase in aqueous solution was quantitatively examined by using Fourier transform infrared (FT-IR) spectroscopy and resolution enhancement techniques were combined with band curve-fitting procedures to quantitate the spectral information from the amide I bands.
Abstract: The secondary structure of streptokinase (Sk) in aqueous solution was quantitatively examined by using Fourier transform infrared (FT-IR) spectroscopy. Resolution enhancement techniques, including Fourier deconvolution and derivative spectroscopy, were combined with band curve-fitting procedures to quantitate the spectral information from the amide I bands. Nine component bands were found under the broad, nearly featureless amide I bands which reflect the presence of various substructures. The relative areas of these component bands indicate an amount of beta-sheet between 30 and 37% and an alpha-helix content of only 12-13% in Sk. Further conformational substructures are assigned to turns (25-26%) and to "random" structures (15-16%). Additionally, the correlation of a pronounced component band near 1640 cm-1 (10-16% fractional area) with the possible presence of 3(10)-helices is discussed.
TL;DR: In this article, a new time-resolved Fourier transform spectrometer that is capable of 0.25 cm−1 spectral resolution and better than 10−7 s temporal resolution in the visible is reported.
Abstract: The development of a new time‐resolved Fourier transform spectrometer that is capable of 0.25 cm−1 spectral resolution and better than 10−7 s temporal resolution in the visible is reported. The time‐resolved capability of the spectrometer is achieved by coupling a step‐scan interferometer to a transient digitizer/laser system. The operation of the spectrometer is described in detail, and scattered light and laser‐induced fluorescence spectra from an I2 gas cell are presented to demonstrate the temporal and spectral resolution of the spectrometer.
TL;DR: It is shown that the resolution for coherent signals can be improved by squaring array covariance matrices before forming smoothed array covariant matrices.
Abstract: Spatial smoothing techniques are used to estimate the directions of coherent arrivals. The performance of these techniques deteriorates rapidly as the coherent arrivals become closely spaced. The author examines the resolution performance of the existing forward-only and forward/backward spatial smoothing techniques. It is shown that the resolution for coherent signals can be improved by squaring array covariance matrices before forming smoothed array covariance matrices. >
TL;DR: There are three classes of interactions between tropomyosin molecules in the spermine-induced crystals and these give some insights into the molecular interactions between coiled-coil molecules that may have implications for assemblies such as muscle thick filaments and intermediate filaments.
TL;DR: A unified treatment of the resolution of three closely related techniques is presented: emission electron microscope, PEM, low energy electron microscopy (LEEM), and mirror electron microscope (MEM), based on the intensity distribution in the image plane for an object of finite size rather than for a point source.
Patent•
29 Jun 1992
TL;DR: In this article, a hysteresis loop is used for mapping high resolution data into lower resolution data using a transparent digitizer, which is disposed above a liquid crystal display.
Abstract: A process for mapping high resolution data into lower resolution data involves the use of a hysteresis loop. A transparent digitizer (22) is disposed above a liquid crystal display (24). As an operator writes on the digitizer (22) with a stylus (26), the writing is digitized to form high resolution data which is converted to lower resolution data utilized to operate the display (24). Distortion resulting from the conversion is minimized by using a hysteresis loop concept wherein change of the lower resolution data is prevented unless there is at least a given minimum change in the high resolution data, the value of the lower resolution data also depending on whether the high resolution data is increasing or decreasing in value.
02 Feb 1992-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, an elastic recoil detection analysis technique with swift heavy ions was developed to measure high resolution depth profiles of light elements in thin films and multilayer systems, achieving a depth resolution of 1 nm with a Q3D magnetic spectrograph using a high quality 120 MeV 197Au12 beam.
Abstract: An elastic recoil detection analysis technique with swift heavy ions has been developed to measure high resolution depth profiles of light elements in thin films and multilayer systems. A depth resolution of 1 nm was achieved with a Q3D magnetic spectrograph using a high quality 120 MeV 197Au12 beam. The depth resolution was tested with 12C recoil ions from 12C/11B multilayers. Due to the large solid angle used (2 msr) and large scattering cross sections only low ion currents ( ≈ 109ionss) are necessary for good statistics within a few minutes of irradiation. The method was applied to depth profile analysis of light elements in a-Si:H/a-SiC:H multilayer systems. Alterations in the multilayers induced by the heavy ion beam have been observed during long lasting irradiations and might limit the depth resolution when profiling small elemental concentrations.
TL;DR: Using FTIR microscopy with polarized IR radiation on silicalite I single crystals fully loaded with p-xylene, the existence of an ordered adsorbate was proven for the first time by IR spectroscopy.
Abstract: Using FTIR microscopy with polarized IR radiation on silicalite I single crystals fully loaded with p-xylene, the existence of an ordered adsorbate could be proven for the first time by IR spectroscopy. By analyzing the polarized absorption bands the orientation of the p-xylene molecules relative to the host structure could be determined. The results agree well with structural data obtained from X-ray diffraction experiments. These first results suggest that polarized IR microscopy could develop into a powerful tool for the analysis of adsorbate structures, assisting in complete structure resolution by diffraction techniques
TL;DR: In this article, a critical discussion of the computational methods of Fourier resolution enhancement (band narrowing) and their role in the analysis of the infrared absorption spectra of proteins is presented.
Abstract: Publisher Summary This chapter presents a critical discussion of the computational methods of Fourier resolution enhancement (band narrowing) and their role in the analysis of the infrared absorption spectra of proteins. This type of numerical data processing does not affect the instrumental resolution but changes the shape of the infrared bands and, by reducing their width, allows a better visual separation (that is, resolution) of individual component bands. One area of biology in which infrared spectroscopy has become particularly useful is the structural analysis of proteins and, in particular, the determination of the secondary structure of soluble and membrane-bound proteins. There are two common methods of resolution enhancement via band narrowing that use the Fourier transform: Fourier self-deconvolution (FSD) and Fourier derivation (FD). The chapter discusses a number of practical considerations in the application of the numerical computer methods for band narrowing. The Fourier resolution enhancement in applications may be employed to advantage on any data set that satisfies two criteria: (1) high S/N ratio and (2) composite bands with intrinsic widths that are large as compared to the instrumental resolution.
TL;DR: The idea of solving many of the basic problems in electron microscopy by means of electron holography is straightforward as discussed by the authors, however, with the progress in experimental realization of EH at high resolution, severe difficulties show up and the major obstacle in reaching 0.1 nm resolution seems to be the imprecise knowledge about the aberrations of the microscope.
TL;DR: In this paper, the limits imposed by photon statistics on the resolution attainable by deconvolving seeing-broadened astronomical images are investigated and an approximate analytic theory is given that predicts the dependence of resolution thus defined on the number of detected photons.
Abstract: The limits imposed by photon statistics on the resolution attainable by deconvolving seeing-broadened astronomical images are investigated. By analogy with the classical Rayleigh limit for diffraction-limited images, resolution is defined as the separation of the equal component double star that can be just resolved by deconvolution. An approximate analytic theory is given that predicts the dependence of resolution thus defined on the number of detected photons, and this theory is tested by deconvolution experiments on synthetic images
TL;DR: In this paper, a high-resolution fluorescence spectrometer using a Johann geometry in a backscattering arrangement was developed, with a resolution of 0.3 eV at 6.5 keV.
Abstract: A high‐resolution fluorescence spectrometer using a Johann geometry in a backscattering arrangement was developed. The spectrometer, with a resolution of 0.3 eV at 6.5 keV, combined with an incident beam, with a resolution of 0.7 eV, form the basis of a high‐resolution instrument for measuring x‐ray absorption spectra. The advantages of the instrument are illustrated with the near‐edge absorption spectrum of dysprosium nitrate.
TL;DR: In this paper, high spatial resolution Auger electron spectra and scanning Auger microscope (SAM) images of supported metal catalysts have been obtained in a UHV scanning transmission electron microscope.
TL;DR: In this paper, new instrumental developments are described, based on STEM optics and through-the-lens electron detection, which allow scanning Auger electron microscopy (SAM) to be performed at the nanometer level.
TL;DR: In this paper, the filtered backpropagation algorithm of diffraction tomography is generalized to include evanescent wave components of the data in the reconstruction process, and a methodology is presented for determining the convolutional filters required in the algorithm to achieve any given spatial resolution.
Abstract: The filtered backpropagation algorithm of diffraction tomography is generalized to include evanescent wave components of the data in the reconstruction process. A methodology is presented for determining the convolutional filters required in the algorithm to achieve any given (specified) spatial resolution in the reconstruction. The point spread functions of the algorithm with both optimal and sub-optimal filters are presented and indicate that significant improvement in resolution can be obtained by incorporation of evanescent waves in the reconstruction. Stability and noise sensitivity of the reconstruction procedure is discussed.
02 Feb 1992-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, a high-resolution electrostatic spectrometer for MeV ions and its use for investigating surfaces and near-surface layers of solids by high resolution Rutherford backscattering spectroscopy (HRBS) was described.
Abstract: The paper reports on a high-resolution electrostatic spectrometer for MeV ions and its use for investigating surfaces and near-surface layers of solids by high-resolution Rutherford backscattering spectroscopy (HRBS). The spectrometer has been set up at the 6 MV Pelletron accelerator of the Max-Planck-Institut fur Metallforschung, Stuttgart, over the last few years and has recently been operated successfully. The instrument consists of a cylinder type, 100° electrostatic analyzer (radius: 700 mm, gap width: 20 mm) and a system of electrostatic quadrupole lenses which focus those ions emitted from the target parallel to the optical axis onto the entrance slit of the analyzer, thus minimizing kinematic errors in the energy resolution. A variable slit system allows one to choose between a maximum in energy resolution or in ion count rate. The analyzed ions are registered simultaneously with a position sensitive Si-surface barrier detector. The maximum ion energy to be analyzed is about 2 MeV for singly charged ions. The relative energy resolution of the instrument is better than 3 × 10−4. The overall resolution as obtained in an actual HRBS measurement with 1 MeV 4He+ ions amounts to 1.44 keV, thus providing a depth resolution of 0.88 nm at ion incidence of 22.5° to the surface normal or 0.17 nm for oblique incidence of the ion beam (10° to the normal) in Au. Besides the description of the spectrometer and its capabilities, this paper will give examples of various applications. They include studies of the oxidation of metal surfaces, of island formation on surfaces, and of electron capture processes of fast ions in the near surface region.
TL;DR: A tantalum x-ray laser is used together with an x-rays zone plate lens to image a test pattern and paves the way to three dimensional biological imaging with high spatial resolution (20-30 nm).
Abstract: High-brightness and short-pulse-width (~200 ps) x-ray lasers offer biologists the possibility of high-resolution three-dimensional imaging of specimens in an aqueous environment without the blurring effects associated with natural motions. As a first step toward developing the capabilities of this type of x-ray microscopy we have used a tantalum x-ray laser (λ = 4.483 nm) together with an x-ray zone plate lens to image a test pattern. The observed image shows a detector-limited resolution of approximately 75 nm and paves the way to three-dimensional biological imaging with high spatial resolution (20–30 nm).
TL;DR: In this paper, the authors describe the solution and refinement of Ga2(HPO3)3.4H2O, a framework structure with 29 atoms in the asymmetric unit cell and 117 structural parameters, by the combined use of synchrotron X-ray and neutron powder diffraction.
Abstract: THE feasibility of determining crystal structures from powder diffraction data has improved substantially during the past decade. Early work using laboratory X-ray data1,2 has been followed by studies that take advantage of the higher resolution provided by synchrotron X-ray3 and neutron4 diffraction instrumentation. Other advances have been made in the computational aspects of the problem5,6. Nevertheless, there has remained a disparity between the complexity of structures that can be solved, ab initio, from powder data, and those that can in principle be refined by the Rietveld profile method7. For example, refinements with up to 34 atoms8 and 132 positional parameters9 have been reported, but the most complex unknown structure to be solved from powder data contains only 17 atoms in the asymmetric unit cell10. Here we describe the solution and refinement of Ga2(HPO3)3.4H2O, a novel framework structure with 29 atoms in the asymmetric unit cell and 117 structural parameters, by the combined use of synchrotron X-ray and neutron powder diffraction. Exploiting the complementary nature of these techniques further extends the power of powder diffraction for structure determination.