Window of transparency

The free-base form of sapphyrin also displays three relatively weak Q-type transitions in the 620-710 nm region of the visible spectrum. On protonation, these bands increase in intensity, and are generally blue-shifted to between 615 and 690 nm. Depending upon which acid is used, the number of Q-bands observed for protonated sapphyrins varies from two to four in number. These bands too are red-shifted relative to the Q-bands of porphyrins. In fact, because of this bathochromic shifting, the sapphyrins actually absorb light at the edge of the physiological window of transparency that occurs between ca. 100 and 900 nm. This makes sapphyrin... 

For a discussion of the desirability of long-wavelength photosensitizers and their relevance to the so-called physiological window of transparency , see Kreimer-Birnbaum, M. Semin. Hematol. 1989, 26, 157-173. 

A further advantage of the CE system is that unlike the TE, a window of transparent material can be incorporated into... 

It is clear that processing must address both loss (with impurities in the parts per billion range) and fiber structure designed to minimize dispersion. Figure 4 shows the window of transparency for high silica fiber. At short wavelengths, loss is bounded by ultraviolet... 

Hydrocarbons, such as hexane, heptane, and isooctane, may be used, but they have reduced solvent powers and are typically limited in use for the dissolution of nonpolar materials (the old rule of like-dissolves-like applies here). More polar solvent, such as alcohols (methanol, ethanol, isopropyl alcohol, etc.), dioxane, tetrahydrofuran, sulfolane, and dimethyl formamide, may be used for special applications, but it must be realized that the spectra of these solvents are very intense and often quite complex. As a result, there are limited windows of transparency at which measurements may be made. A number of excellent spectral collections have been published that feature solvent spectra (27-31), and it is recommended that the reader consult one of these texts before proceeding with a solvent-based method. 

Initially, DADC polymers were used in military aircraft for windows of fuel and deicer-fluid gauges and in glass-fiber laminates for wing reinforcements of B-17 bombers. Usage in impact-resistant, lightweight eyewear lenses has grown rapidly and is now the principal appHcation. Other uses include safety shields, filters for photographic and electronic equipment, transparent enclosures, equipment for office, laboratory, and hospital use, and for detection of nuclear radiation. 

Transparent polyethylene can be also applied to the protection of window glass against aggressive media, e.g., the effect of hydrogen fluoride on the plants producing superphosphate fertilizers. The use of transparent polyethylene film for window glass makes it possible to cut down on the heat losses due to the lower thermal conductance of polyethylene as compared to glass. 

Fig. 6. Comparison of the responses of two grasses of contrasted growth rate and morphology to five intensities of shoot impedance, (a) Lolium perenne b) Festuca ovina. Each curve records the mean progress of shoot expansion in five replicate plants subjected to standardised resistances (indicated on each curve as the force in newtons required for initial deflection of weighted windows). Plants were grown individually within a transparent cone, from which the shoots, in order to escape, must deflect windows of standard dimensions and angle of inclination.

External reflectance. The most commonly applied in situ IR techniques involve the external reflectance approach. These methods seek to minimise the strong solvent absorption by simply pressing a reflective working electrode against the IR transparent window of the electrochemical cell. The result is a thin layer of electrolyte trapped between electrode and window usually 1 to 50 pm. A typical thin layer cell is shown in Figure 2.40. 

The sample is dissolved in 1-5 % of the solvent and it is then placed in a solution cell consisting of transparent windows of alkali metal halides. A second cell containing pure solvent is then placed in the path of reference beam to cancel out solvent interferences. 

In recent years, the use of transparent fuel cells has increased substantially due to the need for a better understanding of liquid water accumulation on the surface of the DLs and flow through the FF channels. In most transparent cells, either the cathode or the anode (or both) has transparent polycarbonate end plates that act as windows and sit on top of the corresponding FF plates. These plates are normally thin and made out of metal, such as stainless steel or gold-plated brass, and their thickness is equal to the depth of the FF channels (i.e., the charmels are machined all the way through the plate). Thus, the transparent end plate also acts as part of the charmels. 

The cornea is the transparent window of the eye it is 500 pm thick at the centre and histologically made of, from the snrface to the inside ... 

Solomon took me by the hand and led me through a wine cellar into a secret but very stately hall, where he refreshed me with flowers and apples, but its windows were made out of transparent crystals and I looked through them. And he said "What dost thou see "... 

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