Showing papers on "Resolution (electron density) published in 1991"

Breaking the Diffraction Barrier: Optical Microscopy on a Nanometric Scale

Abstract: In near-field scanning optical microscopy, a light source or detector with dimensions less than the wavelength (lambda) is placed in close proximity (lambda/50) to a sample to generate images with resolution better than the diffraction limit. A near-field probe has been developed that yields a resolution of approximately 12 nm ( approximately lambda/43) and signals approximately 10(4)- to 10(6)-fold larger than those reported previously. In addition, image contrast is demonstrated to be highly polarization dependent. With these probes, near-field microscopy appears poised to fulfill its promise by combining the power of optical characterization methods with nanometric spatial resolution.

X-ray diffraction data collection system for modern protein crystallography with a Weissenberg camera and an imaging plate using synchrotron radiation

Abstract: The X-ray diffraction data collection system, with a Weissenberg camera, an imaging plate, and image reader BA100, using SR was constructed in the Photon Factory for protein crystallography. It allows us to collect a full data set with one crystal in 2.5 h by rotation of a sample around a single axis. The high accuracy and extended resolution of the collected data were confirmed by comparison with the data obtained from other detectors and results from the structure determination. Further improvements in the function and accuracy of this system are discussed.

The Effect of DEM Resolution of Slope and Aspect Mapping

Abstract: This article examines the effect of the spatial resolution of digital elevation models (DEMs) on slope and aspect data. After a review of computing methods for slope and aspect and such factors as DEM resolution, topographic complexity, and quality of DEM data, the article presents two experiments using DEMs from 8 to 80 m intervals. Results of the experiments show that the accuracy of slope and aspect data, as well as the mean and standard deviation of slope values, decrease with lower DEM resolutions. Comparison of slope and aspect maps generated from different resolutions reveals that slope differences concentrate in areas of steep slopes, whereas aspect differences are in generally flat areas with minor landform features. Slope differences can be explained statistically by relative relief, and aspect differences by relative relief and standard deviation of elevation.

Spontaneous Resolution by Stirred Crystallization

Abstract: It does not take long for a beginning chemist to develop a naive trust in predictions based on probability. Unlike a physician, who deals with a handful of cases, or an epidemiologist, who deals with hundreds of thousands, a chemist has the luxury of dealing with samples that contain more than lo2’ molecules. For such large samples, predictions based on probability verge on certainty. Chemists are not disturbed that quantum mechanics precludes strict determinism in the behavior of an individual molecule, because it supplies reliable probabilities, and for macroscopic chemical samples molecular probability amounts to collective determinism. A chemist who has difficulty repeating a literature experiment may attribute the problem to unobserved or unreported differences in procedure or materials, or to error in measurement, but not to sampling error. The precise reproducibility from experiment to experiment that is the hallmark of good chemistry depends on having samples with enormous numbers of molecules. Because of their training, chemists are particularly intrigued by phenomena that seem improbable. Several such cases involve chirality. A familiar and profound example is the occurrence in nature of only one enantiomer of complex biological molecules. How did living systems become resolved? Does biological handedness result from some weak interaction that provided a tiny evolutionary bias in favor of one set of enantiomers, or from one single molecular event that occurred at random but was destined to become a sort of molecular “Adam” by being multiplied into the whole kingdom of living things? Crystallization provides a more homely example of curious statistics involving chirality. Although growth of a macroscopic crystal involves a large number of molecular events, formation of the original nucleus occurs but once per crystal. It is not uncommon for a solution to deposit only one crystal. Even if 100 or 1000 crystals grow, the number of nucleation events is small by chemical standards, and they differ from most chemical phenomena in that they can often be counted individually as well as measured collectively. Recently, Dilip Kondepudi et al. of Wake Forest University (USA) have reported results from counting chiral crystals that provide new insights into the mechanism of nucleation.“] Their interest in the role of competition and autocatalysis in breaking chiral symmetry in the biosphere,L2’ led Kondepudi et al. to repeat 19th Century work by Kipping and Pope on the crystallization of NaCIO, . I3] This salt is particularly well suited for such experimentation because aqueous solutions of its achiral ions produce beautiful rectangular prisms in the chiral cubic space group P2,3. Since the individual ions are achiral, they can join either enantiomeric

Atomic resolution scanning tunneling microscopy images of Au(111) surfaces in air and polar organic solvents

Abstract: Atomic features of a close‐packed metal surface have been observed for the first time by scanning tunneling microscopy in organic polar solvents. Evaporated gold films, exhibiting large reconstructed (111) terraces, have been imaged with a resolution far superior to previous results in aqueous environments.

The influence of specimen refractive index, detector signal integration, and non-uniform scan speed on the imaging properties in confocal microscopy

Abstract: SUMMARY Refraction of light in a specimen volume may cause aberrations that influence the imaging properties in confocal microscopy In this paper the influence on three-dimensional resolution and geometry is experimentally investigated for a uniform specimen volume It is found that the depth resolution is more severely affected than the lateral resolution This is unfortunate, because even under ideal conditions the depth resolution is lower than the lateral resolution Lateral image geometry is little affected by the specimen refractive index, whereas the depth scale can be considerably elongated or compressed The influence of a finite detector integration time is also considered This can give a noticeable, but not particularly severe effect on the image resolution in the line-scan direction Because the integration time can be accurately controlled, a shorter integration time can be used when maximum resolution is essential, albeit at the price of a higher noise level In scanning fluorescence microscopy a non-uniform scan speed may give large variations in bleaching over the specimen surface Experiments illustrate how serious such non-uniform bleaching effects can be when a specimen area is repeatedly scanned, for example when recording optical serial sections

Multiple resolution machine readable symbols

Abstract: A multiple resolution optically encoded label is readable at two more optical resolutions, and is able to store two or more respective channels of optically encoded 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.

Scanning tunneling microscopy on rough surfaces‐quantitative image analysis

Abstract: In this communication, the application of scanning tunneling microscopy (STM) for a quantitative evaluation of roughnesses and mean island sizes of polycrystalline thin films is discussed. Provided strong conditions concerning the resolution are satisfied, the results are in good agreement with standard techniques as, for example, transmission electron microscopy. Owing to its high resolution, STM can supply a better characterization of surfaces than established methods, especially concerning the roughness. Microscopic interpretations of surface dependent physical properties thus can be considerably improved by a quantitative analysis of STM images.

Applications of confocal scanning optical microscopy to dentistry.

Abstract: Confocal optical microscopy is now a well recognised technique in the fields of biological and materials science. This type of light microscope can be considered as being midway between optical and electron microscopy. Confocal or scanning optical microscopes can make high resolution, thin, optical sections within semitransparent samples such as biological tissues. Surface images of samples can be produced which are similar in character to those of the SEM, but without many of the problems of specimen preparation. The improved resolution and removal of out-of-focus blur allows much more information to be gained from fluorescence microscopy techniques, with the images capable of 3-D reconstruction of the sample. There are basically two types of confocal optical microscope: the laser scanning type (CLSM) and the real-time direct view of tandem scanning microscopes (TSM). The former are best suited to immunofluorescence microscopy, whilst the latter are more appropriate for high-speed reflection imaging, having originally been developed for in vivo microscopy.

Method of selectable resolution magnetic resonance imaging

Abstract: Multi-slice selectable resolution NMR data acquisition in which multiple slice regions in an object are defined, and the slice regions are excited to emit NMR signals. The NMR signals are spatially encoded, and at least two selected slice regions are excited to emit NMR signals encoded with different spatial resolutions.

Three-dimensional structure of myosin subfragment-1 from electron microscopy of sectioned crystals.

Abstract: Image analysis of electron micrographs of thin-sectioned myosin subfragment-1 (S1) crystals has been used to determine the structure of the myosin head at approximately 25-A resolution. Previous work established that the unit cell of type I crystals of myosin S1 contains eight molecules arranged with orthorhombic space group symmetry P212121 and provided preliminary information on the size and shape of the myosin head (Winkelmann, D. A., H. Mekeel, and I. Rayment. 1985. J. Mol. Biol. 181:487-501). We have applied a systematic method of data collection by electron microscopy to reconstruct the three-dimensional (3D) structure of the S1 crystal lattice. Electron micrographs of thin sections were recorded at angles of up to 50 degrees by tilting the sections about the two orthogonal unit cell axes in sections cut perpendicular to the three major crystallographic axes. The data from six separate tilt series were merged to form a complete data set for 3D reconstruction. This approach has yielded an electron density map of the unit cell of the S1 crystals of sufficient detail. to delineate the molecular envelope of the myosin head. Myosin S1 has a tadpole-shaped molecular envelope that is very similar in appearance to the pear-shaped myosin heads observed by electron microscopy of rotary-shadowed and negatively stained myosin. The molecule is divided into essentially three morphological domains: a large domain on one end of the molecule corresponding to approximately 60% of the total molecular volume, a smaller central domain of approximately 30% of the volume that is separated from the larger domain by a cleft on one side of the molecule, and the smallest domain corresponding to a thin tail-like region containing approximately 10% of the volume. This molecular organization supports models of force generation by myosin which invoke conformational mobility at interdomain junctions within the head.

X-ray optics. 2: A technique for high resolution spectroscopy

Abstract: A novel combination of optical elements and properties is combined to achieve high spectral resolution using grazing incidence optics of modest quality. We show through analysis and ray tracing of examples that using radial groove gratings at high blaze angles in the manner of an echelle spectrograph can provide high spectral resolution. We compare this arrangement to the conventional in-plane designs and show the off-plane to be superior in nearly every respect. Cross dispersion can be provided by the energy resolution of a CCD detector. Then, we show how additional resolution can be squeezed from the system by strategic placement of gratings to take advantage of the azimuthal response of a Wolter x-ray optic. With a telescope that has only 30-sec of arc imaging we are able to support resolution lambda/deltalambda of 3000, while a conventional design at the same graze angle supports resolution of only 200.

Microscopic view of scanning tunneling microscopy

Abstract: We present a theory of the atomic resolution in scanning tunneling microscopy (STM) in terms of localized surface states on the tip. The tunneling matrix elements arising from these tip states are evaluated with the derivative rule. For example, a pz surface state on the tip generates a tunneling matrix element proportional to [∂ψ/∂z] at the nucleus of the apex atom, and a d3z2−r 2 tip state generates a tunneling matrix element proportional to [3∂2ψ/∂z2−κ2ψ], (ψ is the sample wave function, κ is the decay constant of surface wave function, κ=(2meφ)1/2/ℏ ). To obtain analytic results of theoretical STM images, we further developed a simple independent‐orbital model to describe the wave functions of the sample surface. With this model, we present qualitative and quantitative explanations of the observed atomic resolution on metals and semiconductors, the spontaneous switching of instrument resolution during imaging, and various tip‐sharpening procedures.

Water structure in cubic insulin crystals

Abstract: The electron density distribution of the solvent in the cubic insulin crystal structure, which occupies 65% of the volume, has been mapped from 1.7-A resolution diffraction data by an iterative difference Fourier method, using the previously determined protein structure as the refinement restraint. Starting with phases from the protein and a flat solvent model, the difference map calculated from the data was added outside the protein envelope, and the modified map was then used to recalculate phases for the iterative refinement. Tests of the method with model data, with the experimental data and a variant protein model, and by carrying out a partial refinement of the solvent map demonstrate that the refinement algorithm produces reliable values for the solvent density within the noise level of the data. Fluctuations in density are observed throughout the solvent space, demonstrating that nonrandom arrangements of the water molecules extend several layers from the well-ordered hydration shell in contact with the protein surface. Such ordering may account for the hydration force opposing close approach of hydrophilic surfaces and other long-range water-dependent interactions in living structures.

Correction of aberrations of an electron microscope by means of electron holography

Abstract: Electron holography using the M\"ollenstedt-type electron biprism [G. M\"ollenstedt and H. D\"uker, Z. Phys. 145, 377 (1956)] is now able to improve resolution and expressiveness of the electron microscope by subsequent correction of its aberrations and unique determination of amplitude and phase, as suggested by Gabor.

X-ray microscope

Abstract: An x-ray microscope in which the object is illuminated coherently or partially coherently via a condenser with quasi-monochromatic x-radiation and is imaged enlarged in the image plane by a high resolution x-ray objective. To obtain the highest possible image contrast, there is arranged in the Fourier plane of the x-ray objective an element which imparts a phase shift to a preselected order of diffraction of the radiation. The element extends over the surface region in the Fourier plane which is acted on here by the diffracted radiation to be influenced. The utilization of the phase shift of a preselected order of diffraction of the radiation as compared with the uninfluenced radiation makes it possible to carry out examinations, in particular of biological structures, with a low dose of radiation and nevertheless to produce a high image contrast. Moreover, it is possible to shift the wavelength region of the x-ray radiation to be used toward shorter wavelengths at which, as a result of the lesser absorption, x-ray microscopy was not meaningfully possible heretofore.

A Recommended Specific Definition of “Resolution”

Abstract: 1991 b: Surface airtemperature response to increasing gJobal industrial productivity: A beneficial greenhouse effect? a: Effects of two and a half years of atmospheric CO2 enrichment on the root density distribution of three-year-oldsourorangetrees. 1991 b: Downward regulation of photosynthesis and growth at high CO2 levels: No evidehce for either phenomenon in three-year study of sour orange trees. a CO2\"fertilization effect of the terrestrial vegetation to the amplitude increase in atmospheric CO2 at Mauna Loa Ob-The annual variation of atmospheric CO2 concentration observed in the northern hemisphere. 1960: Accumulation of organic matter in a chronosequence of soils developed on wihd-blown sand in New Zealand. 1991: Root restriction as a factor in photosynthetic acclimation of cotton seedlings groWn in elevated carbon dioxide. The term, \"resolution,\" has been used in a wide variety of peer-reviewed publications to refer to the grid increment used in a model. For example, general circulation models (GCMs) are said to have a resolution of about 400 km by 400 km, when that scale more appropriately refers to the horizontal grid mesh. From sampling theory, it is well known, however, that at least two grid increments are required to represent data. Real information at scales smaller than two grid increments are erroneously aliased to larger scales. An illustration of this is presented in Pielke (1984, Fig. 10.7). Models such as GCMs, however, require additional grid resolution to adequately simulate meteorological processes as a result of serious computational inaccuracies at scales less than four grid increments (e.g., see Table 10.1, 10.2, and 10.3 in Pielke 1984). Some investigators suggest even more grid increments are needed for adequate simulations. Using these clarifications, resolution within a numerical model should refer to at least four times the grid interval. For instance, a GCM with 400 km by 400 km horizontal grid increments would have a resolution of no less than 1600 km by 1600 km. Diagnostic data (e.g., terrain) with sampling ata400-km interval would have a resolution of no better than 800 km.

X-ray microscopes.

Abstract: The new x-ray microscopes considerably improve on the resolution of optical microscopes. They can also be used to map the distribution of certain chemical elements. Some can form pictures in extremely short times, and some hold the promise of special capabilities such as three-dimensional imaging. Unlike conventional electron microscopy, x-ray microscopy enables specimens to be kept in air and in water, which means that biological samples can be studied under conditions similar to their natural state. The illumination used, so-called soft x rays in the wavelength range of 20 to 40 angstroms (an angstrom is one ten-billionth of a meter), is also sufficiently penetrating to image intact biological cells in many cases. Because of the wavelength of the x rays used, soft x-ray microscopes will never match the highest resolution possible with electron microscopes. Rather their special properties will make possible investigations that will complement those performed with light- and electron-based instruments.

Magnetically induced super resolution in a novel magneto-optical disk

Abstract: A super resolution has been achieved in the magneto-optical disk using an exchange-coupled multilayer film. Two types of magnetically induced super resolution, front aperture detection and rear aperture detection have been successfully investigated. A high C/N of more than 42 dB is obtained experimentally for a mark length of 0.3 micrometers which is much shorter than the resolution limit expected from the conventional diffraction theory.