Density-based discrimination of protein and RNA in the ribosome

1992 ◽  
Vol 50 (1) ◽  
pp. 464-465
Author(s):  
Joachim Frank
Keyword(s):  
Transfer Function ◽  
Spatial Frequency ◽  
Three Dimensional ◽  
Wiener Filter ◽  
Dark Field Image ◽  
Dark Field ◽  
Frequency Range ◽  
Bright Field ◽  
Contrast Transfer Function ◽  
Pass Filter

Cryo-electron microscopy combined with single-particle reconstruction techniques has allowed us to form a three-dimensional image of the Escherichia coli ribosome.In the interior, we observe strong density variations which may be attributed to the difference in scattering density between ribosomal RNA (rRNA) and protein. This identification can only be tentative, and lacks quantitation at this stage, because of the nature of image formation by bright field phase contrast. Apart from limiting the resolution, the contrast transfer function acts as a high-pass filter which produces edge enhancement effects that can explain at least part of the observed variations. As a step toward a more quantitative analysis, it is necessary to correct the transfer function in the low-spatial-frequency range. Unfortunately, it is in that range where Fourier components unrelated to elastic bright-field imaging are found, and a Wiener-filter type restoration would lead to incorrect results. Depending upon the thickness of the ice layer, a varying contribution to the Fourier components in the low-spatial-frequency range originates from an “inelastic dark field” image. The only prospect to obtain quantitatively interpretable images (i.e., which would allow discrimination between rRNA and protein by application of a density threshold set to the average RNA scattering density may therefore lie in the use of energy-filtering microscopes.

Imaging of platinum-shadowed macromolecular complexes in dark field

1984 ◽  
Vol 42 ◽  
pp. 146-147
Author(s):  
D.W. Andrews ◽  
F.P. Ottensmeyer
Keyword(s):  
Thin Film ◽  
Three Dimensional ◽  
Average Diameter ◽  
Dark Field ◽  
Bright Field ◽  
Field Mode ◽  
Macromolecular Complexes ◽  
Average Mass ◽  
Topological Features ◽  
Projection Images

Shadowing with heavy metals has been used for many years to enhance the topological features of biological macromolecular complexes. The three dimensional features present in directionaly shadowed specimens often simplifies interpretation of projection images provided by other techniques. One difficulty with the method is the relatively large amount of metal used to achieve sufficient contrast in bright field images. Thick shadow films are undesirable because they decrease resolution due to an increased tendency for microcrystalline aggregates to form, because decoration artefacts become more severe and increased cap thickness makes estimation of dimensions more uncertain.The large increase in contrast provided by the dark field mode of imaging allows the use of shadow replicas with a much lower average mass thickness. To form the images in Fig. 1, latex spheres of 0.087 μ average diameter were unidirectionally shadowed with platinum carbon (Pt-C) and a thin film of carbon was indirectly evaporated on the specimen as a support.

Spatial Frequency Domain Analysis of Heat Transfer in Microelectronic Chips With Applications to Temperature Aware Computing

2007 ◽  
Author(s):  
Keivan Etessam-Yazdani ◽  
Hendrik F. Hamann ◽  
Mehdi Asheghi
Keyword(s):  
Transfer Function ◽  
Spatial Frequency ◽  
Frequency Domain ◽  
Thermal Power ◽  
Three Dimensional ◽  
Heat Removal ◽  
Frequency Domain Analysis ◽  
Heat Diffusion ◽  
The Impact ◽  
Spatial Frequency Domain

In this paper we present a novel analytical approach for obtaining the thermal transfer function of multi-layer chips in the spatial frequency domain. The behavior of the transfer function is used to address a number of key issues such as 1) the appropriate power granularity required for microarchitecture thermal-power analysis, and 2) the impact of packaging and cooling solutions on heat removal from chip hotspots. The merit of the presented method is in 1) simplicity, such that even for rather complicated multi-layer structures the analysis takes only a fraction of a second, and 2) accuracy, because the approach is based on the exact solution of three-dimensional heat diffusion equations.

Structures and defects identified by dark-field HREM

1992 ◽  
Vol 50 (1) ◽  
pp. 124-125
Author(s):  
J.P. Zhang
Keyword(s):  
High Resolution ◽  
Structural Information ◽  
Image Interpretation ◽  
Dark Field Image ◽  
Dark Field ◽  
Bright Field ◽  
Field Mode ◽  
Transmitted Beam ◽  
Structure Information ◽  
The Difference

The tilted illumination dark field high resolution imaging technique was applied to structures and defects of semiconductors and superconductors. We used a Hitachi-H9000 top entry microscope with a high resolution pole-piece of Cs=0.9 mm, operated at 300 Kv. Proper apertures, tilting angle and imaging conditions were chosen to minimize the phase shift due to aberrations. Since the transmitted beam was moved outside the aperture, the noise ratio was greatly reduced, which resulted in a significant enhancement of image contrast and apparent resolution. Images are not difficult to interpret if they have a clear correspondence to structure - information from image simulations in bright field mode can be used to assist in dark field image interpretation.An example in a semiconductor, GaAs/Ga0.49In0.51P2 superlattice imaged along [110] direction is shown in Figure 1. In this dark field image the GaAs and GaInP layers can be easily distinguished by their different contrast, and the difference in quality between both sides of interfaces is clear. An enlarged image in Figure 1 shows the defective area on the rough side of interface. Since this image shows the same pattern as the [110] projection of an fee structure, the major structural information about {111}, {200}, {220} planes can be obtained from this zone. Note that in bright field mode, [110] is not a good zone for imaging such multilayers.

Characterization of Low Frequency Combustion Dynamics of Hot Blast Stoves by Means of a Flame Transfer Function Based on CFD Forced Response Simulations: Comparison of Different Hot Blast Stove Designs

2015 ◽  
Author(s):  
Simon Gövert ◽  
Virginia Fratalocchi ◽  
Jim B. W. Kok
Keyword(s):  
Transfer Function ◽  
Mass Flow ◽  
Forced Response ◽  
Computational Time ◽  
Band Pass Filter ◽  
Computational Domain ◽  
Frequency Range ◽  
Pass Filter ◽  
Combustion Dynamics ◽  
Hot Blast

The combustion dynamics of thermo-acoustic systems like gas turbine combustors at elevated pressure and atmospheric industrial furnaces can be studied using a forced response approach. In this approach, the flame is excited by external perturbation of the upstream fuel or air mass flow. The flame transfer function can then be determined, which describes the response of the heat release rate in the combustor or furnace to the upstream velocity fluctuations. Subsequently, the flame transfer function can be used as an input for acoustic network models to further analyze the stability behavior of a given combustion system. Most of the applications of the flame transfer function analysis are for natural gas fired systems with dimensions such, that most of the relevant combustion dynamics is in the frequency range 100–500 Hz. The situation is different for hot blast stoves as used in the iron making process. Here the fuel is low calorific coal gas and the dimensions of the stove are huge, with heights of 30 m at a diameter of 5 m. This leads to a relevant frequency range for the combustion dynamics in interaction with acoustics of about 3–80 Hz. In order to cope with this combination of a large computational domain and extreme low frequent combustion dynamics in the response simulation, special attention was devoted to computational efficiency. In order to allow for a sufficient mesh resolution to capture the combustion characteristics while keeping the computational demands in a feasible range, the computational domain is to be drastically reduced by the use of symmetry assumptions. In a first step, the mesh dependency is studied and different combustion models are analyzed for a reference geometry on the basis of steady states results. The burning velocity model with adapted laminar flame speed description is subsequently chosen for the transient simulations. Transient numerical simulations are performed using a URANS turbulence model. The combustor is excited by a multi-harmonic perturbation of the fuel mass flow, to further reduce computational time. The flame transfer function is determined and compared for two different burner designs. The results show significant impact of combustor design on the acoustic behavior and combustion time scales. While the reference design acts like a low pass filter with a cut-off frequency of about 6 Hz, the modified design shows band-pass filter characteristics with a lower and higher cut-off frequency of 30 and 60 Hz, respectively.

A Transfer Function Description of Sheet Metal Forming for Process Control

1991 ◽  
Vol 113 (1) ◽  
pp. 44-52 ◽  
Author(s):  
R. D. Webb ◽  
D. E. Hardt
Keyword(s):  
Transfer Function ◽  
Process Control ◽  
Spatial Frequency ◽  
Sheet Metal ◽  
Closed Loop ◽  
Control Method ◽  
Three Dimensional ◽  
Identification Problem ◽  
Complex Deformation ◽  
Domain Transfer

Three-dimensional forming of sheet metal parts is typically accomplished using one or two shaped tools (dies) that impart the necessary complex curvature and induce sufficient in-plane strain for part strength and shape stability. This research proposes a method of applying closed-loop process control concepts to sheet forming in a manner that automatically converges upon the appropriate tooling design. The problem of controlling complex deformation is reduced to a system identification problem where the die-part transformation is developed as a spatial frequency domain transfer function. This transfer function is simply the ratio of the measured change in spatial frequency content of the part and the die. It is then shown that such a transfer function can be used to implement closed-loop process control via rapid die redesign. Axisymmetric forming experiments are presented that establish the appropriateness of the linear transfer function description (via a test of superposition) and demonstrate the convergence properties of the proposed control method.

Principles and Technique of Fluorescence Microscopy

1961 ◽  
Vol s3-102 (60) ◽  
pp. 419-449
Author(s):  
M. R. YOUNG
Keyword(s):  
Fluorescence Microscopy ◽  
Focal Length ◽  
Dark Field Image ◽  
Wide Band ◽  
Dark Field ◽  
Microscopical Study ◽  
Light Sources ◽  
Bright Field ◽  
Alternative Systems ◽  
Light Filters

Interest in fluorescence microscopy has greatly increased in recent years. Technical considerations have to some extent prevented even wider application of the various fluorescence techniques now available for microscopical study of biological specimens. This paper outlines the basic requirements for optimal image quality, for the benefit of biologists and others who may not be conversant with the optical principles involved. The central problem of illumination is reviewed in some detail, and an assessment given of the two methods in current use, namely the bright-field and dark-field systems. Ratios of fluorescent to activating light received by the objective aperture, given by the two systems, have been compared, and measurements have been made of their relative light-concentrating power. Available light sources and their suitability for the excitation of fluorescence are discussed, with the problems of selecting appropriate light filters for use with the alternative systems of illumination. It is concluded that the dark-field system has decided advantages in practice and in theory for the following reasons: (1) The dark-field condenser serves as an efficient primary filter, contributing to a black background and hence good contrast. (2) The equivalent focal length is less than that of the bright-field condenser and it concentrates energy in a smaller area; this compensates in part for the loss of energy inevitably caused by the central stop. (3) It permits the use of wide-band primary filters of maximum transmission because contrast in the fluorescent image is affected only by a weak superimposed dark-field image produced in the object-plane by scattered residual activating light passed by the primary filter. With blue-light activation the visible dark-field image is effectively eliminated by means of a weak blue-absorbing secondary filter. (4) The loss of contrast due to veiling glare is minimized. A rational layout for fluorescence microscopy and methods for accurate alignment of the microscope in the vertical and horizontal positions are described. Factors influencing the choice of suitable objectives and eyepieces and some details of methods for mounting specimens are given.

Displaced Aperture Dark Field Images by an Aberration Correction

1972 ◽  
Vol 30 ◽  
pp. 564-565
Author(s):  
K. Shirota ◽  
T. Yamamoto ◽  
T. Yanaka ◽  
O. Vingsbo
Keyword(s):  
Optical Axis ◽  
Dark Field Image ◽  
Image Plane ◽  
Dark Field ◽  
Objective Lens ◽  
Aberration Correction ◽  
Bright Field ◽  
Incident Electron Beam ◽  
Dark Field Microscopy ◽  
Electron Orbit

In displaced aperture dark field microscopy, the direction of the incident electron beam with respect to the specimen is maintained unaltered between bright field and dark field images, unlike the case of usual high resolution dark field microscopy by tilted illumination. The displaced aperture technique, however, gives a strong dark field image deterioration due to field aberrations. These are prounouncedly large since the deviation of the orbits of the imaging electrons from the optical axis is very large in this case. In the present paper, the improvement of the image quality by aberration correction is discussed.1. The chromatic field aberration is composed of components mainly from the objective and intermediate lenses. It can be corrected by changing the electron orbit by means of a beam deflector, introduced in the image plane of the objective lens.

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