Showing papers on "Resolution (electron density) published in 1986"

Near‐field optical‐scanning microscopy

Abstract: Near‐field optical‐scanning (NFOS) microscopy or ‘‘optical stethoscopy’’ provides images with resolution in the 20‐nm range, i.e., a very small fraction of an optical wavelength. Scan images of metal films with fine structures presented in this paper convincingly demonstrate this resolution capability. Design of an NFOS microscope with tunnel distance regulation, its theoretical background, application potential, and limitations are discussed.

Resolution-enhanced Fourier transform infrared spectroscopy of enzymes.

Abstract: Publisher Summary This chapter describes the basic principles, techniques, and applications of resolution-enhanced Fourier transform infrared spectroscopy. Infrared spectroscopy constitutes one of the oldest methods for studying the secondary structure of polypeptides and proteins. Polypeptides and proteins exhibit a total of nine characteristic absorption bands in the infrared region. These are usually termed the amide A, B, and amide I-VII bands. The amide I (∼1630-1690 cm -1 ) band is the most useful for protein structure studies by infrared spectroscopy. The use of Fourier transform infrared spectroscopy (FTIR) has led to major improvements in this regard. In principle, FTIR provides several advantages over conventional dispersive techniques: higher (1) resolution, (2) sensitivity, (3) signal-to-noise ratio (S/N), and (4) frequency accuracy. Any one of the first three advantages can be emphasized at the expense of the other two. For protein structure studies, high sensitivity makes it possible to acquire usable infrared spectra of aqueous solutions; such spectra are always notoriously difficult to obtain.

Principles of analytical electron microscopy

Abstract: This text discusses the fundamentals which lay a foundation for today's state-of-the-art microscopy. All currently important areas in analytical electron microscopy--including electron optics, electron beam/specimen interactions, image formation, x-ray microanalysis, energy-loss spectroscopy, electron diffraction and specimen effects--have been given thorough attention.

Super-resolution fluorescence near-field scanning optical microscopy

Abstract: A one‐dimensional near‐field scanning optical microscope (NSOM) operating in the fluorescence mode has been demonstrated. NSOM line scans of both metallic edges and fluorescent gratings have been obtained and quantitatively compared to both scanning electron micrographs and conventional optical micrographs of the same structures. The sharpness of the near‐field scans indicates resolution of <100 nm.

Information capacity and resolution in an optical system

Abstract: The concept of invariance of information capacity is discussed and applied to the resolution of an optical system. Methods of obtaining superresolution in microscopy are discussed, and scanning microscopy has many distinct advantages for such applications.

The rotationally resolved electronic spectrum of indole in the gas phase

Abstract: The high resolution ultraviolet fluorescence excitation spectrum of indole in a supersonic jet has been measured. It was possible to resolve the rotational structure with an experimental resolution of 180 MHz. The details of the technique employed to achieve this resolution in the ultraviolet are described. Analysis of the high resolution spectrum yielded a transition moment direction which is compared to previous theoretical predictions. Application of high resolution spectroscopy to the problem of distinguishing the 1La and 1Lb electronic states in indole and indole derivatives is discussed. From the measured rotational constants possible geometries for the ground and excited states were also determined.

The refined structure of beef liver catalase at 2·5 Å resolution

Abstract: The crystal structure of beef liver catalase [Murthy, Reid, Sicignano, Tanaka & Rossmann (1981). J. Mol. Biol. 152, 465-499] has now been refined by a restrained parameter least-squares method [Konnert & Hendrickson (1980). Acta Cryst. A36, 344-350] with respect to 2.5 A data. Some extra density was discovered during the refinement process. This was interpreted in terms of a bound NADP molecule [Kirkman & Gaetani (1984). Proc. Natl Acad. Sci. USA, 81, 4343-4348; Fita & Rossmann (1985). Proc. Natl Acad. Sci. USA, 82, 1604-1608]. When the noncrystallographic symmetry was imposed as a constraint, the R factor was reduced to 21.2%. However, refinement of the two crystallographic independent subunits gave a final R factor of 19.1%. The refined coordinates have been re-analyzed for main-chain and side-chain hydrogen bonding, charge distribution, secondary structural element interactions, subunit contacts and molecular packing. The fractional accessibility and the temperature-factor variation are also discussed. The oligomerization process is considered in terms of the unusual quaternary structure. The organization of the heme channel and its relation to the enzyme's catalytic properties have been discussed elsewhere [Fita & Rossmann (1985). J. Mol. Biol. 185, 21-37].

Cryo-electron microscopy and three-dimensional reconstruction of actin filaments.

Abstract: Actin filaments have been examined by electron microscopy whilst in a frozen-hydrated state. Filaments embedded in a vitreous water layer are basically similar to those prepared by negative staining and show characteristic helical substructure, where the pitches of the helices are about 70 nm and 6 nm. Variability in spacing between long pitch helix cross-over points has been observed, which is consistent with intrinsic angular disorder between successive filament subunits. Fourier transforms of the most ordered filaments show four strong layer lines that index as the first, fifth, sixth and seventh orders of a 35 nm repeat. A three-dimensional helical reconstruction, calculated to a resolution of about 4 nm, shows the individual subunits to be orientated with their long axes roughly perpendicular to the filament axis. Each subunit is somewhat curved and is resolved into two domains. Most connections between successive subunits appear to be made close to the filament axis. We also report on the performance of the specimen holder (Philips PW 5699) used in this work.

Electron diffraction phenomena observed with a high resolution STEM instrument

Abstract: Because of the high brightness of the cold field emission source used in a dedicated scanning transmission electron microscopy (STEM) instrument, it is possible to focus electrons to a cross-over of width 3A or less and, with a suitable detection system, to obtain diffraction patterns from specimen regions of this size or greater. Coherent interference effects are visible in shadow images (in-line holograms) and in convergent beam diffraction patterns. Special techniques have been developed for gathering information from the diffraction patterns for application to the study of the structures of crystal defects, crystal surfaces and small particles. Possibilities have been explored for holographic reconstruction from shadow images.

Measurement of optical phase with subpicosecond resolution by time domain interferometry (A)

Abstract: A new and extremely general interferometric technique has been experimentally demonstrated that permits the direct measurement of optical phase on a subpicosecond time scale. The intensity is characterized by cross correlation, and thus the optical field is completely determined.

Determination of depth resolution from measured sputtering profiles of multilayer structures: Equations and approximations

Abstract: Etablissement d'equations permettant la determination de la resolution a partir de mesures des profils de pulverisation; discussion des possibilites d'application et des erreurs introduites en fonction du rapport entre la resolution et l'epaisseur des couches elementaires

X-ray position detection in the region of 6 μm RMS with wire proportional chambers

Abstract: We have developed a MWPC system for X-ray detection with a position resolution in the region of 6 μm rms (14 μm fwhm). The performance with argon, krypton or xenon at pressures from 1 to 10 atm is explored for the X-ray energy range 5–25 keV. At a resolution of 6 μm rms the effects of photoelectron and Auger electron range, electronic noise, avalanche spread, lateral electron diffusion, as well as X-ray beam collimation, become of comparable magnitude. Their limiting effects on avalanche centroid fluctuation, and hence on position resolution, are investigated. The position resolution achieved in this work compares favorably with that of solid state devices.

Metal Deposition by High-Energy Sputtering for High Magnification Electron Microscopy

Abstract: Visualization of fine structures of macromolecular dimensions is an important and growing field of modern biological electron microscopy which was until recently exclusively dominated by transmission electron microscopy. However, only specimen domains of subcellular dimensions can be imaged with the transmission electron microscope (TEM) because of instrumental limitations of tilt angles (±60°) and specimen thickness (< 50–100 nm). Specimens compatible with these limitations are replicas of freeze-etched hydrated cells and cell components and deep-etched or dried preparations of isolated molecules. Recent progress made in the development of scanning electron microscopic imaging methods now makes it possible to use also modern scanning electron microscopes (SEM) for high magnification, secondary electron (SE) imaging. Resolution may be increased to dimensions equal to electron beam probe diameters of <1 nm. This improved SEM resolution is similar to that obtained with TEM replicas. The increased SEM tilt capability (±90°) and the high depth of focus, obtained by adjusting the focus while scanning the image (dynamic focusing), enables the SEM to reveal macromolecular fine structures in dried bulk specimens not only of whole single cells but also of complex tissues.