Critical wavelength

Water-cooled x-ray tubes, 249 Wavelength, critical absorption, discussion, 16-18... 

The fact that the absorption coefficient depends on the wavelength critically affects the determination of the amount of intensity absorbed. In addition, Lambert-Beer s law is limited to dilute solutions. In Eq. (3) only the absorption of the reactant A is considered. However, the decrease in intensity is caused by all light-absorbing components in the solution. For this reason, the amount of light absorbed by all reactants in the solution is given by... 

Unlike absorbers, tjrpical quenchers do not need high absorption at the wavelengths critical for polymer degradation, although they may exert some shielding effect on the UV light. 

An even wider range of wavelength, toward the infrared, can be covered with quantum well lasers. In the Al Ga As system, compressively strained wells of Ga In As are used. This ternary system is indicated in Figure 6 by the line joining GaAs and In As. In most cases the A1 fraction is quite small, X < 0.2. Such wells are under compressive strain and their thickness must be carefully controlled in order not to exceed the critical layer thickness. Lasers prepared in this way are characterized by unusually low threshold current density, as low as ca 50 A/cm (l )-... 

The i j -configuration of the 6,7-double bond in pre-vitamin D is critical to its subsequent thermal rearrangement to the active vitamin. A photochemical isomerization of pre-vitamin D to yield the inactive trans-isoTnen occurs under conditions of synthesis, and is especially detrimental if there is a significant short wavelength component, eg, 254 nm, to the radiation continuum used to effect the synthesis. This side reaction reduces overall yield of the process and limits conversion yields to ca 60% (71). Photochemical reconversion of the inactive side product, tachysterol, to pre-vitamin D allows recovery of the product which would otherwise be lost, and improves economics of the overall process (70). 

In the 1990s hplc has become widely used in the flavor and fragrance industry to measure vanillin and other phenoHc compounds. Routine methods have been developed that are particularly adapted to thermosensitive products, such as vanillin and its derivative products, with elution gradient and uv detection at given wavelengths. Certain critical impurities can thus routinely be traced to very low (10 ppm) concentrations. 

If a fluctuation has a wavelength which is less dran this critical value, it will not be stable but will decay. 

The degree of attenuation at the critical frequency can be very large, but this type of silencer has a very narrow bandwidth. This device may be suitable when the machine being dealt with emits sound predominantly of a single wavelength. Lining the chamber with absorbers can expand the absorber bandwidth of a Helmholtz resonator, but this has the effect of reducing the efficiency. The perforated absorber, which forms the basis of many acoustic enclosures and silencers, is a development of the resonator principle. 

The effective wavelength provides a useful way of characterizing polychromatic beams that are not appreciably affected by the presence of an absorption edge. One suspects intuitively that the presence of an absorption edge critically located could cause complications in absorptiometry with polychromatic beams. That this does happen has been demonstrated,13 and it limits the usefulness of the effective wavelength. 

---