Wire frame

Fig. II-1. A soap film stretched across a wire frame with one movable side.

As a point of interest, it is possible to form very thin films or membranes in water, that is, to have the water-film-water system. Thus a solution of lipid can be stretched on an underwater wire frame and, on thinning, the film goes through a succession of interference colors and may end up as a black film of 60-90 A thickness [109]. The situation is reminiscent of soap films in air (see Section XIV-9) it also represents a potentially important modeling of biological membranes. A theoretical model has been discussed by Good [110]. 

The most well-known and at the same time the earliest computer model for a molecular structure representation is a wire frame model (Figure 2-123a). This model is also known under other names such as line model or Drciding model [199]. It shows the individual bonds and the angles formed between these bonds. The bonds of a molecule are represented by colored vector lines and the color is derived from the atom type definition. This simple method does not display atoms, but atom positions can be derived from the end and branching points of the wire frame model. In addition, the bond orders between two atoms can be expressed by the number of lines. 

The capped sticks model can be seen as a variation of the wire frame model, where the structure is represented by thicker cylindrical bonds (figure 2-123b). The atoms are shi unk to the diameter of the cylinder and ai e used only for smoothing or closing the ends of the tubes. With its thicker bonds, the capped sticks model conveys an improved 3D impression of a molecule when compared with the wire frame model. 

Figure 2-123. The most coinmon molecular graphics representations of phenylalanine a) wire frame b) capped sticks c) balls and sticks d) space-filling.

In order to represent 3D molecular models it is necessary to supply structure files with 3D information (e.g., pdb, xyz, df, mol, etc.. If structures from a structure editor are used directly, the files do not normally include 3D data. Indusion of such data can be achieved only via 3D structure generators, force-field calculations, etc. 3D structures can then be represented in various display modes, e.g., wire frame, balls and sticks, space-filling (see Section 2.11). Proteins are visualized by various representations of helices, / -strains, or tertiary structures. An additional feature is the ability to color the atoms according to subunits, temperature, or chain types. During all such operations the molecule can be interactively moved, rotated, or zoomed by the user. 

Tube and wire frames are used to protect windows, skylights and similar glass areas and constitute a high level of security but may be aesthetically unacceptable. 

Figure 2. Transition state complex in the ethanol + 2-pentanol 8, 2 reaction activated by the proton at the chaimel intersection of H21SM-5 [14]. The zeolite pore structure is represented as a wire-frame section of the intersecting channels produced by the MAPLE V software package. The zeolite proton that activates the 2-pentanol molecule is marked with. ...

Fig. 2.3.2 A wire frame drawing and photograph of a Mark I GARFieid magnet as manufactured by Resonance Instruments Ltd. The third picture is a close up of the sample space.

To extend these calculations to cylinders is more complicated, as both the position and orientation of a cylinder must be obtained. To do that we followed the sequence of operations used to position each cylinder, as shown in Fig. 32a, for particle 1, the lower front particle in the wall segment (note that wire frames of the previous positions are retained in each sketch for comparison). Similar sequences were available for each of the other particles in the wall segment model. 

Figure 2.8 Part of a polyethylene oxide chain using wire frame and space-filling models.

Fig. 39) lay the tube on a small wire frame on the left-hand pan of the balance. The frame supports the tube at two points. Then put on the counterpoise (always use the same weights as counter-... 

Now open the cocks on the absorption apparatus and the cock on the aspirator, and make sure that the previously determined rate of flow of the bubbles in the counter is maintained. A difference of 1-2 units in the number of bubbles passing in ten seconds has no detrimental effect. If necessary, restore the former rate of flow of the bubbles by lowering or raising the levelling tube of the aspirator. (Collect the water which drops from the aspirator during the analysis in a 500 c.c. measuring cylinder). Then place in position the copper-wire frame which conducts the heat from the furnace to the constricted part of the tube and to the side tube of the calcium chloride tube so that the metal touches the glass. Condensation of water in the side tubes is thus absolutely prevented. 

The state of surface energy has also been described by the following classic example (Adamson and Gast, 1997 Chattoraj and Birdi, 1984 Birdi, 1989 Birdi, 1997,2002). Consider the area of a liquid film that is stretched in a wire frame by an increment dA, whereby the surface energy changes by (y dA) (Figure 2.2). Under this process, the opposing force is f. From these data on dimensions, we find that... 

There is another point of view from which it is often useful to regard surface phenomena. If the surface of a soap-film in a wire frame is increased by moving outwards against the tension one side of the frame, a quantity of work must be done against the surface tension equal to the product of the surface tension and the increase of area. A definite quantity of potential energy is thus bound up with each unit of surface. The numerical value of the surface energy defined as energy per unit surface is clearly the same as that of the surface tension. The dimensions in each case are... 

Figure 2.2 Diagram of a soap film stretched on a wire frame.

You go to the blackboard and begin to sketch. There s another way to draw a hypercube. Notice that if you look at a wire-frame model of a cube with its face directly in front of you, you will see a square within a... 

Figure 4.5 A wire-frame model of a cube viewed head-on and a tesseract.

A two-dimensional analog of PV work can be recognized in fluid films that exhibit surface tension (tendency of the film surface to contract against an opposing spreading force). The surface tension work wsurf (of, for example, a soap film) can be measured by a rectangular wire-frame device with moveable edge, as shown in Fig. 3.5. 

Figure 3.5 Wire-frame device with sliding edge (length L) for measuring the surface tension work Wsurf of a soap film of area A and surface tension y.

Spheres are drawn as semi-transparent objects, with a wire frame on their surface to enhance the impression of depth and to make it easier to judge the size of the spheres in the third dimension (Fig. 6.6). 

Consider a liquid film constrained by a wire frame and moveable slide wire as shown in Figure 3.2. Assuming the entire system is frictionless, the surface tension... 

Figure 3.2 Forces involved in stretching a thin liquid film, held in a wire frame, by pulling on one side via a slide-wire.

To illustrate, consider a simplified surface geometry, a soap film that is stretched on a wire frame (see Figure 3.2). For small areal changes, the dynamic tension difference A /d between the starting and ending positions can be approximated by using the surface elasticity, EM,... 

Fig. 3. Examples of 5-HT3 agonist and antagonist pharmacophores. Serotonin (A) and granisetron (B) are shown as examples of 5-HT3 receptor agonists and antagonists. Both molecules are shown as stick models. Electrostatic potential is displayed in wire frame. Attention has been drawn to the important features of each pharmacophore.

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