Ring illumination

The first use of SORS in the area of noninvasive probing of bones was reported by Schulmerich et al. [25]. The team succeeded in the recovery of the Raman spectra of bones transcutaneously from depths of several millimeters in animal and human cadavers. Subsequently, with improved instrumentation based around a ring illumination geometry (equivalent to inverse SORS), Schulmerich et al. [29] reached another key milestone demonstrating the feasibility of measuring Raman spectra noninvasively from a depth of 4 mm from chicken tibia with better than 8% accuracy in terms of the relative Raman band intensities between the... 

Figure 1. Light optical micrographs of (a) plan view of a corrosion pit in a nickel alloy tube, with concentric ring illumination, at a magnification of lOX, and (b) cross section of a corrosion pit in copper metal with the same illumination and 25X magnification.

The Silverman ring illuminator, is still available from E. Leitz. It is a circular array of small light sources, again fitting around the objective so that light is directed downward from all sides onto the surface. 

Microscope accessories. If videotaping the responses, use a good high-resolution camera (Hitachi, KPM-1) attached to the dissecting microscope via a C-mount adaptor. A ring illuminator (various stock numbers to fit on the microscope objective, Edmund Scientific) fitted to a fiber-optic illuminator provides even and shadow-free illumination. 

Proton-proton coupling constants of benzo rings of benzazoles can illuminate the bonding in such compounds. Thus, comparison of the J values for naphthalene with those for benzotriazoles of different types (Table 13) shows evidence of bond fixation, particularly in the 2-methyl derivative (98) (71PMH(4)l2l). 

TEM offers two methods of specimen observation, diffraction mode and image mode. In diffraction mode, an electron diffraction pattern is obtained on the fluorescent screen, originating from the sample area illuminated by the electron beam. The diffraction pattern is entirely equivalent to an X-ray diffraction pattern a single crystal will produce a spot pattern on the screen, a polycrystal will produce a powder or ring pattern (assuming the illuminated area includes a sufficient quantity of crystallites), and a glassy or amorphous material will produce a series of diffuse halos. 

Under illumination, some of the luciferin molecules (LnH) that absorbed photons are changed into free radicals (Ln ), probably at carbon-2 of the imidazopyrazinone ring. The free radical instantly binds with an oxygen molecule to form a peroxide radical (LnOO ), an extremely fast reaction (k = 109M 1 s"1 Pryor, 1976). The peroxide radical formed reacts with a luciferin molecule, generating a new free radical of luciferin and a luciferin peroxide anion (LnOO"),... 

It is well known that by inserting an optical amplifier obtained by population inversion in an optical cavity, one can realize sources of coherent radiations, namely lasers. One can operate in the same way with parametric amphfication as shown on Fig. 1. A nonlinear crystal illuminated by an input pump is inserted in an optical cavity. This cavity is represented for convenience as a ring cavity but consists usually of a linear cavity. An important difference with the laser is that there are three different fields, insfead of one, which are presenf in the amplifying medium, all these fields being able to be recycled by the cavity mirrors. One obtain thus different types of "Optical Parametric Oscillators" or OPOs. 

It can also be mentioned that polyphosphazenes substituted with aromatic groups, such as phenols or naphthols, can form inter- and intra- molecular excimers by coupling reaction of the planar aromatic rings of the substituents under illumination [467-471,473,725]. These species disappear as soon as the light is switched off. 

When porphyrins dissolved in strong mineral acids or in organic solvents are illuminated by ultraviolet hght, they emit a strong red fluorescence. This fluorescence is so characteristic that it is often used to detect small amounts of free porphyrins. The double bonds joining the pyrrole rings in the porphyrins are responsible for the characteristic absorption and fluorescence of these compounds these double bonds are absent in the porphyrinogens. 

FIG. 16 Photocurrent spectra corresponding to the photo-oxidation of DCMFc by ZnYPPC" at the water-DCE interface under chopped illumination and lock-in detection. The main features of the spectra coincide with the onset of the Soret band and the Q-bands of the porphyrin ring. (From Ref. 73. Reproduced by permission of the Royal Society of Chemistry.)... 

It is instructive, however, and even illuminating, to consider the EM s for a few hypothetical gas-phase reactions for which such EM s can be calculated from the available thermodynamic data. Before doing this, however, it is useful to examine briefly the thermodynamic properties of ring vs open-chain... 

Dark-field illumination is classified into three types. The first one is for a microscope equipped with low numerical aperture (NA) objective lenses (see Fig. 1). To cast a shadow at the objective lens, a ring-slit as shown in Fig. IB is inserted into the light path. The second is for highNA (>0.5) objective lenses. Special, ready-made dark-field condensers or lenses are used for dark-field illumination. The third is independent... 

As described before, special built-in equipment is not always necessary for dark-field microscopy, and one can readily convert bright-field illumination to dark-field illumination. An inverted microscope equipped with long-distance (low NA) lenses is suitable for setup of a dark-fieldmicroscope. A handmade ring-slit is available when objective lenses such as x4 lens withNA 0.13, xlO lens withNA 0.30, and x20 lens... 

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