Displays raster

As the graphical capabilities of the computer systems became more powerful simultaneously the number of visualized structures increased. With the introduction of raster graphics (1974) and colored raster graphics displays (1979), other forms of molecular representations were possible [197]. CPK models could be represented and colored bonds or molecular surfaces could be visualized. 

Often, more detailed information is needed on the distribution of a constituent. The technique of X-ray area scanning, or dot mappings can provide a qualirative view of elemental distributions. As the beam is scanned in a raster pattern on the specimen, a cathode ray rube scanned in synchronism is used to display a full white dot whenever the X-ray detector (WDS or EDS) detects an X ray within a certain narrow energy range. The pattern of dots is recorded on film to produce the dot map. Dot maps are subject to the following limitations ... 

If the analyzer is set to accept electrons of an energy characteristic of a particular element, and if the incident X-ray beam is rastered over the surface to be analyzed, a visual display the intensity of which is modulated by the peak intensity will correspond to the distribution of that element over the surface. The result is also an image and this technique is realized with the Quantum 2000. 

Imaging SIMS, used for spatially resolved elemental analysis. A focussed ion beam is rastered over the surface so that each point on the target is individually bombarded in turn, so that secondary ion emission is localized. The intensity of a particular secondary ion is monitored for each position of the primary beam and the result shown at the corresponding point of a synchronized oscilloscope display or computerized data system. In this way, pixel by pixel across the sample surface and in depth as the material is removed, three-dimensional information on the sample composition may be obtained. 

We have kept the data collection computer and its software simple and economical. The computing power and peripherals needed to provide high quality plotting and data reduction are available on a 32-bit minicomputer that supports a number of our projects. The floppy discs from the data collection process can be read directly into the data reduction computer. Special menus have been set up to facilitate plotting of the data on a high speed color raster display or on a high-quality multicolor pen plotter. 

Figure 1.4 Effects of MnPN stimulation on EEG patttern and PLH neuronal activity. Upper An MnPN 6 s stimulus train suppressed PLH neuronal discharge, evoked EEG synchronization, and reduced EMG activity. The sweep display shows effects of successive stimulus trains. The events display shows averaged PLH neuronal discharge rate in conjunction with train stimulation. Lower Raster plot showing neuronal discharge during single pulse stimulation. In this example, PLH neuronal activity was inhibited with a latency of about 10 ms inhibition lasted about 110 ms. Activation of MnPN neurons during NREM sleep would result in suppression of PLH neuronal activity.

At the same time, the power and capabilities of standard PCs increased dramatically. The Richardsons (Richardson and Richardson, 1992) at Duke University developed molecular graphics programs to run on the Macintosh. In a dramatic development, the World Wide Web emerged. Roger Sayle created RasMol as part of his PhD dissertation at Oxford, and made the source code freely available on the web. This program allowed raster display of molecules on UNIX or PCs. The RasMol... 

This type of electron microscope is completely different in principle and application from the conventional transmission-type electron microscope. In the scanning instrument, the surface of a solid sample is bombarded with a fine probe of electrons, generally less than 100 A in diameter. The sample emits secondary electrons that are generated by the action of the primary beam. These secondary electrons are collected and amplified by the instrument. Since the beam strikes only one point on the sample at a lime, the beam must be scanned over the sample surface in a raster pattern to generate a picture of the surface sample. The picture is displayed on a cathode ray tube from which it can be photographed. 

The displays used in the last section are usually raster devices due the the need for a variety of colors or shading options. The resolution of... 

The CRT displays are usually vector devices, usually of high resolution (1024 x 1024) to provide clean lines. Raster equipment with its lower resolution and "jaggies" does not provide any advantage until we add the complexity of the solid fill for surfaces, or a range of colors. Hardcopy - frequently pen plotters -is a normal requirement. 

CRT displays can be broken down into two categories vector and raster technologies. A vector is a line drawn from some current position to a new one. This type of display is also referred to as a "random scan" device since the pattern of painting the screen depends on the figure drawn. With raster systems, the vector is interpreted as the dots (their position) needed to draw it. In addition, raster devices paint the screen in a ordered fashion, regardless of the resulting image. 

Raster technology provides a different approach to CRT graphics. Raster devices have one thing in common with vector refresh displays - they must be updated 60 times a second. But rather than moving a beam between... 

Its not difficult to see why the jaggies occur. To begin with, lets go back to that piece of graph paper. This time we will pay attention to the boxes on the paper rather than the lines. Each box - or pixel - is the addressable element in the display. If we want to draw a line on the paper in the manner of the raster display, pick boxes for the endpoints (a diagonal shows the problem best) and draw a straight line connecting the centers of those boxes. Now shade in... 

Color is another factor in raster displays. Using vector systems we were limited to a single color against a dark background, here we have more flexibility. By adding more memory in the form of additional planes, we can store more information about each pixel. With only one plane, we can tell if that pixel should be illuminated or not, giving a monochrome black-and-white display. The second plane... 

Many elements of a controlled vocabulary are effectively defined by software implementation. Thus, the description of the HTML language requires certain elements to have specified behavior. For example, supports the display of raster images, but the precise look may vary between implementations and file types. Implementation through software is useful and powerful where authors, publishers, readers, and processors all use the same system. Because STM publishing is increasingly multidisciplinary, this implementation becomes problematic. Often a reader may have to download specialist software that is idiosyncratic and that may not have enough functionality, especially the export of semantically rich data. Moreover, the semantic rules are often buried deep in the software and difficult to understand precisely. 

Irradiation. Samples were irradiated with electrons in the preparation chamber. The electron accelerating voltage was 3 keV. The beam current was 0.7 fiA and was measured by directing the beam into a hole in the sample support which was biased 30 volts positive. After the beam current was stable, the specimen was placed on the support and the beam was rastered over an area of 1.3 cm which covered the entire PTFE surface, and an absorbed-current image of the specimen was displayed. 

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