Shadow-casting

Figure 1.1 is a rather remarkable photograph which shows individual polystyrene molecules as spherical blobs having average diameters of about 20 nm. The picture is an electron micrograph in which a 10" % solution of polystyrene was deposited on a suitable substrate, the solvent evaporated, and the contrast enhanced by shadow casting. There is a brief discussion of both electron microscopy and shadowing in Sec. 4.7. Several points should be noted in connection with Fig. 1.1 ...

Figure 1,1 Individual polystyrene molecules as seen in an electron microscope. Tails are the result of shadow casting, which is used to enhance the visibility of the particles. [From M. J. Richardson, Proc. Royal Soc. 279A 50 (1964).]...

Figure 4.11 Electron micrographs of polyethylene crystals, (a) Dark-field illumination shows crystals to have a hollow pyramid structure. (Reprinted with permission from P. H. Geil, Polymer Single Crystals, Interscience, New York, 1963.) (b) Transmission micrograph in which contrast is enhanced by shadow casting [Reprinted with permission from D. H. Reneker and P. H. Geil, /. Appl. Phys. 31 1916 (I960).]...

Radiation transmission methods, in which thickness is determined by (measured as) the shadow cast from a radioactive source, are limited to... 

A pole which casts a 15-foot-long shadow stands near an 8-foot-high stop sign. If the shadow cast by the sign is 3 feet long, how high is the pole ... 

Fig. 3. Shadows cast by simple solidprofiles. It can be seen that the shadows cast in positive and negative replicas are not interchangeable in either shape or tone. (From ref. [54] with permission.)...

People are invisible to radio waves. In other words, there should be no effect when standing between a radio-wave transmitter and its receiver. Conversely, humans are not invisible to light in the wavelength range 100-1000 nm - we say they are opaque, which is most easily proved by asking a person to stand in the path of a light source such as a torch, and seeing the shadow cast. 

A woman, 64 inches tall, casts a shadow that is 51.2 inches long. If the length of the shadow cast by the flagpole is 192 inches, how tall is the flagpole ... 

After the Bride [in the Large Glass] make a picture of shadows cast from objects, [cast] first on a plane and [then] upon a surface with such and such a curvature [and] thirdly upon several transparent surfaces. One can thereby obtain a hypo-physical analysis of successive transformation... 

FIG. 1.12 Electron micrograph of two different types of particles that represent extreme variations from spherical particles (a) tobacco mosaic virus particles (Photograph courtesy of Carl Zeiss, Inc., New York) and (b) clay particles (sodium kaolinite) of mean diameter 0.2 fim (by matching circular fields). In both (a) and (b), contrast has been enhanced by shadow casting (see Section 1.6a.2a and Figure 1.21). (Adapted from M. D. Luh and R. A. Bader, J. Colloid Interface Sci. 33, 539(1970). 

Price, T. M., Strong, D. D., Rudee, M. L., and Doolittle, R. F. (1981). Shadow-cast electron microscopy of fibrinogen with antibody fragments bound to specific regions. Proc. Natl. Acad. Sci. USA 78, 200-204. 

Insoluble surface films can be studied by electron microscopy. The films are transferred from the substrate on to a collodion support and shadow-cast by a beam of metal atoms directed at an angle a (about 15°) to the surface (Figure 4.21). If the width x of the uncoated region is measured, the thickness of the film, x tan a, can be calculated for example, a /i-C36H73COOH film has been shown to be about 5 nm thick - i.e. consistent with a vertically orientated monomolecular layer. The technique has also been used for following the state of the surface as a film is compressed. 

The size of the projectile is well represented by its mean presented area, i.e., the mean area of its shadow cast on a plane averaged over all possible orientations. An appropriate scaling model can be derived for penetration, although the derivation is beyond the scope of this paper. The result may be expressed as... 

The alignment of the patches does not agree with the direction of the shadow cast by the crematorium chimney ... 

After she d gone, I lay in my old bed and watched the cushiony shadows cast by the firelight. At first I heard her creep about, then, when she was settled, a shifting and cracking of boards as the house rearranged itself. From somewhere deep in the woods came the screech of an owl. 

The x-ray technique for crystals, however, is not the same as that of a medical or dental x-ray. In the case of a medical or dental x-ray, the x-rays are allowed to pass through the body and the images are of the shadow cast by the dense tissue—bones or teeth—that the x-rays could not penetrate. X-ray studies of crystals (called x-ray crystallography) look at reflected x-rays, rather than transmitted x-rays, and analyze the patterns in the reflected rays. 

Radiation transmission methods, in which thickness is determined by (measured as) the shadow cast from a radioactive source, are limited to pieces of equipment small enough to be illuminated by small radioactive sources. There are several schemes for highlighting cracks. If the metal is appropriate, magnetic particles can be used to accentuate cracks. Magnetic particles will congregate along... 

How did chemists greet the new tool made suddenly available to them towards the mid-1950s Their obvious alacrity was tinged with ambivalence. Chemists of the old school did not always embrace the new situation that they were dependent on young upstarts, called NMR specialists . They retrained themselves. They had to. In addition, they had to contend with the shadow cast by physics, which obscured the cherished notion of the autonomy of chemistry, of its non-reducibility to physics. The mixed feeling expressed itself in a catch phrase of those times, physical methods . 

Figure 12.28 Formation of an x-ray diffraction pattern of the protein hemoglobin. A, The sample of crystalline hemoglobin is rotated to obtain many different angles of incoming and diffracted x-rays. B, A diffraction pattern is obtained as a complex series of spots. (Large white spot in center is a shadow cast by the apparatus.) C, Computerized analysis relates the pattern to distances and angles within the crystal. The data are used to generate a picture of the hemoglobin molecule.

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