PET principle

Calixarene containing a dioxotetraaza unit, PET-18, is responsive to transition metal ions like Zn2+ and Ni2+. Interaction of Zn2+ with the amino groups induces a fluorescence enhancement according to the PET principle. In contrast, some fluorescence quenching is observed in the case of Ni2+. PET from the fluorophore to the metal ion is a reasonable explanation but energy transfer by electron exchange (Dexter mechanism) cannot be excluded. 

Fig. 2. Structures of live pH sensors (upper) and PET principle of sensors off-on (bottom). 1 N-(l-bromo-2-naphthylmetliyl) diethanolamine 2 iV-(l-bromo-2-naphthylmethyl)bis(2-chloro-ethyl)amine 3 iV-(l-bromo-2-naphthylmethyl)bis(2-bromoethyl)amine 4 Al-(l-bromo-2-naph-thylmethyl)bis(2-iodoethyl)amine 5 A/, Af -bis(l-bromo-2-naphthylmethyl)diaza-18-crown-6.

The same procedure may be applied in principle to design of forced-recirculation reboilers with shell-side vapor generation. Little is known about two-phase flow on the shell side, out a reasonable estimate of the fric tion pressure drop can be made from the data of Diehl and Unruh [Pet Refiner, 36(10), 147 (1957) 37(10), 124 (1958)]. No void-fraction data are available to permit accurate estimation of the hydrostatic or acceleration terms. Tnese may be roughly estimated by assuming homogeneous flow. 

Another type of fibril substructure in PET fibers, besides the microfibrillar type already discussed, is the lamellar substructure, also referred to as the lateral substructure. The basic structural unit of this kind of substructure is the crystalline lamella. Formation of crystalline lamellae is a result of lateral adjustment of crystalline blocks occurring in neighboring microfibrils on the same level. Particular lamellae are placed laterally in relation to the axis of the fibrils, which explains the name—lateral substructure. The principle of the lamellar substructure is shown in Fig. 2. 

The parallelization of crystallites, occurring as a result of fiber drawing, which consists in assuming by crystallite axes-positions more or less mutually parallel, leads to the development of texture within the fiber. In the case of PET fibers, this is a specific texture, different from that of other kinds of chemical fibers. It is called axial-tilted texture. The occurrence of such a texture is proved by the displacement of x-ray reflexes of paratropic lattice planes in relation to the equator of the texture dif-fractogram and by the deviation from the rectilinear arrangement of oblique diffraction planes. With the preservation of the principle of rotational symmetry, the inclination of all the crystallites axes in relation to the fiber axis is a characteristic of such a type of texture. The angle formed by the axes of particular crystallites (the translation direction of space lattice [c]) and the... 

Measurements of regional cerebral blood flow by PET and of cerebral perfusion by SPECT often detect functional abnormalities before CT or MRI identifies morphological abnormalities 945 The PET method is a valuable tool for the estimation of regional glucose and oxygen metabolic rates and cerebral blood flow 946 PET and SPECT combined with principles of receptor binding permit imaging of receptors in the intact brain 946... 

Basic radiochemistry for PET, SPECT — Principles of labeling with radioisotopes and typical successful ligands. ... 

PET (photoinduced electron transfer) cation sensors 10.3.2.1 Principles... 

PET fluorescent sensors for cations have been highly developed (Bissell et al., 1993). The principle is the same as for PET pH indicators, described in Section 10.2.2.5. 

Most PET fluorescent sensors for cations are based on the principle displayed in Figure 10.7, but other photoinduced electron transfer mechanisms can take place with transition metal ions (Fabbrizzi et al., 1996 Bergonzi et al., 1998). In fact, 3d metals exhibit redox activity and electron transfer can occur from the fluorophore... 

The same design principles apply to the magnesium sensors PET-15 and PET-16, in which the recognition moiety has a smaller cavity . 

In 1959 and 1960, Challa published the first results of quantitative experiments on the poly condensation equilibrium in PET [22, 41, 42], He determined the polycondensation equilibrium constant K at different temperatures and average degrees of polycondensation and found that this parameter depends only slightly on temperature, but increases significantly with increasing degree of polycondensation. The monomer BHET was found not to follow the principle of equal reactivity. 

COMPOUNDING PRINCIPLES FOR PREPARING ENGINEERING-GRADE PET RESINS... 

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