APTE effect

APTE effect 2.step cooperative absorption sensitization... 

In order to illustrate the difference between APTE and cooperative up-conversion, we shall discuss an example of a line-narrowing effect in n-photon summation as a means to distinguish between both processes (Auzel 1984a, 1985). Irradiating Er +-doped samples with IR photons at 1.5 pm leads to various visible emissions. Room-temperature IR F-center laser excitation between 1.4 and 1.6 pm of 10% Er -doped vitroceramic and of Er +iYPs leads to emission bands from near IR to UV. Such emissions may be ascribed to multiphoton excitation of the order of 1 to 5, either by APTE or by the cooperative type, with energy levels of single ions (APTE), or with pair levels, respectively, as illustrated by fig. 23. Successive absorptions in fig. 23 a involve a combination of several J states. The APTE effect, because of self matching by multiphonon processes, involves only and J = Y states. 

Fig. 23. n-photon summation (n= 1,. .., 5) in EP system by (a) cooperative sequential pair absorption, and (b) APTE effect (Auzel 1984a). 

ESA and the APTE effect. The probability for Excited State Absorption (ESA) in a two-step absorption (fVu), connecting a state ) to 3 by the intermediate state E2, is just given by the product of the probabilities for each step... 

For ESA by the APTE effect we have also the product of two energy transfers probabilities. Calculating the rate for the same ESA transition with APTE, it follows... 

In general, fluoride glasses give more metastable levels for a given ion, so more levels could be used as relays in up-conversion either by excited absorption (ESA) or by energy transfers (APTE effect) (see sect. 3.4). As we have seen, this last process is linked with the condition ITsa 1/ c, where IPsa is the transfer probability from ion S to ion A. 

Wea.ther lbillty. One of the more destmctive elements is exposure to sunlight specifically, ultraviolet (uv) light. AH sealants are affected by weathering, but there is much difference in the effect of weathering on different sealants. Most sHicones are stable with respect to uv exposure. Urethanes and polysulfides show effects of uv exposure, but can be formulated with uv absorbers to provide reasonable lifetimes in most appHcations. However, there are exceptions in aH classes of sealants and specifiers must be carehil to look for test data that has proven a specific sealant s durabHity. The source of the test data is also important data from an independent testing laboratory is generaHy apt to be more reHable. 

Inhibition of a regulatory enzyme by a feedback inhibitor does not conform to any normal inhibition pattern, and the feedback inhibitor F bears little structural similarity to A, the substrate for the regulatory enzyme. F apparently acts at a binding site distinct from the substrate-binding site. The term allosteric is apt, because F is sterically dissimilar and, moreover, acts at a site other than the site for S. Its effect is called allosteric Inhibition. 

Nickel, rhodium, palladium, platinum, and Raney cobalt (43) have all been used successfully in reductive alkylations. Platinum is the most used by far (J6). With small carbonyl molecules, such as acetone, palladium is about as effective as platinum, but as the molecular weight increases, platinum is apt to be more effective (SO). 

Hydrogenation of 3-pyridinecarboxylic acids is apt to be accompanied by extensive decarboxylation (2S), but this unwanted reaction can be prevented by carrying out the reaction in the presence of one equivalent of base (33,79). Ruthenium (33), rhodium (29), platinum oxide (2S,59), and palladium (30) have all proved effective catalysts for reduction of pyridinecarboxylic acids to the saturated acid. 

In general, retention decreases as the modifier concentration increases because the modifier competes with the analytes for sites on the stationary phase. The effect on retention of changes in modifier concentration seems to be more pronounced for CSPs than for achiral stationary phases in SFC, and peak shapes are apt to degrade rapidly at low modifier concentrations [12]. Efficiency tends to decrease as the modifier concentration increases because analyte diffusion is slowed by the increased viscosity of the eluent [39]. 

As with other factors, no direct statements can be made relating the reaction of a soil to its corrosive properties. Extremely acid soils (pH 4 0 and lower) can cause rapid corrosion of bare metals of most types. This degree of acidity is not common, being limited to certain-bog soils and soils made acid by large accumulations of acidic plant materials such as needles in a coniferous forest. Most soils range from pH5 0 to pH8 0, and corrosion rates are apt to depend on many other environmental factors rather than soil reaction per se. The 45-year study of underground corrosion conducted by the United States Bureau of Standards included study of the effect of soils of varying pH on different metals, and extensive data were reported. 

Figure 2.4 (A) Pulse sequence for the gated spin-echo (GASPE) or attached proton test (APT) experiment. (B) Effect of the pulse sequence on the C magnetization vectors of a CH group.

Gated decoupling The decoupler is gated during certain pulse NMR experiments, so spin decoupling occurs only when the decoupler is switched on and not when it is switched off used to eliminate either H- C spincoupling or nuclear Overhauser effect in a ID C spectrum, and employed as a standard technique in many other H-NMR experiments, such as APT and y-resolved. 

Here, however, it is possible to obtain stabilization of the low-dense lattice build-up of bulky molecules via intermolecular adhesion and orientation forces. Molecules with planar structural elements are advantageous in this respect since they are apt to support the lattice aggregate, and at the same time they are able to partition off cavities effectively. It is very convenient to use aromatic units. 

In both cases, jige and Apt, as well as jige and piee- are assumed to be parallel to each other. If there is an angle 6 between the corresponding dipole moments ngc and piee>, an effective excited state transition dipole moment should be used instead... 

Existing correlations usually are based on low values of air density, whereas pr can have a significant effect on Apt... 

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