Raster device

Color raster devices A raster device can map an array stored in memory on to the screen so that the value of each element of the array controls the appearance of the corresponding point on the screen. It is possible to draw... 

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... 

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... 

Color raster devices A raster device can map an array stored in memory on to the screen so that the value of each element of the array controls the appearance of the corresponding point on the screen. It is possible to draw each atom as a shaded sphere, or to simulate the appearance of the Corey-Pauling-Koltun (CPK) physical models to maintain most of the famihar color scheme (i.e. C = black, N = blue, O = red, P = Green, and S = yellow). In such representation, atoms are usually opaque, so that only the front layer of atoms is visible. However, clipping with an inner plane or rotation can show the packing in the molecular interior. 

Output. Whereas most early programs sent their output to character-based displays (viz., cathode ray tubes, teletypes, and line printers), modern implementations all assume higher resolution vector or raster devices. 

The scanning tunneling microscope uses an atomically sharp probe tip to map contours of the local density of electronic states on the surface. This is accomplished by monitoring quantum transmission of electrons between the tip and substrate while piezoelectric devices raster the tip relative to the substrate, as shown schematically in Fig. 1 [38]. The remarkable vertical resolution of the device arises from the exponential dependence of the electron tunneling process on the tip-substrate separation, d. In the simplest approximation, the tunneling current, 1, can be simply written in terms of the local density of states (LDOS), ps(z,E), at the Fermi level (E = Ep) of the sample, where V is the bias voltage between the tip and substrate... 

A number of methods are available for the characterization and examination of SAMs as well as for the observation of the reactions with the immobilized biomolecules. Only some of these methods are mentioned briefly here. These include surface plasmon resonance (SPR) [46], quartz crystal microbalance (QCM) [47,48], ellipsometry [12,49], contact angle measurement [50], infrared spectroscopy (FT-IR) [51,52], Raman spectroscopy [53], scanning tunneling microscopy (STM) [54], atomic force microscopy (AFM) [55,56], sum frequency spectroscopy. X-ray photoelectron spectroscopy (XPS) [57, 58], surface acoustic wave and acoustic plate mode devices, confocal imaging and optical microscopy, low-angle X-ray reflectometry, electrochemical methods [59] and Raster electron microscopy [60]. 

The experimental apparatus normally consists of a drawn glass capillary microreference electrode that minimizes screening between anodic and cathodic sites, an apparatus for rastering the microreference electrode across the corroding electrode surface in a systematic manner, high-impedance voltmeters, and the necessary data recording devices. A representative schematic of the apparatus is shown in Fig. 49 (125). The sensitivity and resolution of the measurement depend on the diameter of the tip of the microreference electrode, the standoff distance... 

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. 

Raster units do have some distinct advantages over vector devices ... 

With both vector and raster technologies, there are also the questions of tightly couples vs loosely coupled devices and graphics protocols. 

Terminals tied to a computer through RS232C or 20 mA connections are an example of loosely coupled devices. The serial ASCII transmission of data is adequate for applications where dynamics or animation are not a factor (the VT125 and GIGI can be used to a only very limited extent here). This approach has been used in both classes of equipment, our own terminals for example in raster work and Tektronix or IMLAC terminals in vector systems. 

To acquire an image of the focal plane, the plane has to be scanned in its two lateral directions (x-y directions). To acquire a 3D image of a specimen, the plane images at different vertical positions should also be recorded. A scanning device moves the focal laser spot in the x-y directions on the plane in a regular pattern called a raster. After finishing one scanning plane, the focal spot is moved in the vertical direction to scan a next parallel plane. 

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