Special Circumstances

Drugs are applied to the mucous membranes of the conjunctiva, nasopharynx, and vagina to achieve local effects. On the other hand, the antidiuretic hormone lypressin (Diapid) is given by nasal spray, but the intention is to produce systemic effects. For the treatment of meningeal leukemia, cytosine arabinoside is injected directly into the spinal subarachnoid space. In osteoarthritis, corticosteroids are given by intra-articular injection. 

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It is interesting to note that heuristics 2, 3, and 4 from Sec. 5.2 tend to minimize the flow rate of nonkey components. Heuristic 1 relates to special circumstances when there is a particularly difiicult separation. ... 

A monolayer undergoes a first-order reaction to give products that also form monolayers. An equation that has been used under conditions of constant total area is (t - K°°)/(ifi - t") = exp(-)kr). Discuss what special circumstances are implied if this equation holds. 

Close inspection of equation (A 1.1.45) reveals that, under very special circumstances, the expectation value does not change with time for any system properties that correspond to fixed (static) operator representations. Specifically, if tlie spatial part of the time-dependent wavefiinction is the exact eigenfiinction ). of the Hamiltonian, then Cj(0) = 1 (the zero of time can be chosen arbitrarily) and all other (O) = 0. The second tenn clearly vanishes in these cases, which are known as stationary states. As the name implies, all observable properties of these states do not vary with time. In a stationary state, the energy of the system has a precise value (the corresponding eigenvalue of //) as do observables that are associated with operators that connmite with ft. For all other properties (such as the position and momentum). 

It forms an ion BCI4 only under special circumstances, and never in aqueous solutions (cf. BF3). Like the trifluoride, it is an electron pair acceptor, but the adducts formed tend to decompose more readily. Unlike the corresponding aluminium chloride, boron trichloride exists only as the monomer. 

Substitution can take place by the S l or the 8 2 mechanism elimination by El or E2 How can we predict whether substitution or elimination will be the principal reac tion observed with a particular combination of reactants The two most important fac tors are the structure of the alkyl halide and the basicity of the anion It is useful to approach the question from the premise that the characteristic reaction of alkyl halides with Lewis bases is elimination and that substitution predominates only under certain special circumstances In a typical reaction a typical secondary alkyl halide such as iso propyl bromide reacts with a typical Lewis base such as sodium ethoxide mainly by elimination... 

As crowding at the carbon that bears the leaving group decreases the rate of nude ophilic attack by the Lewis base increases A low level of steric hindrance to approach of the nucleophile is one of the special circumstances that permit substitution to pre dominate and primary alkyl halides react with alkoxide bases by an 8 2 mechanism m preference to E2... 

The development of Eq. (8.49) is based on the approximation given by Eq. (8.46), and the latter is applicable only under the special circumstances cited above. 

Extraction of Nonmetallic Inorganic Compounds. Phosphoric acid is usually formed from phosphate rock by treatment with sulfuric acid, which forms sparingly soluble calcium sulfate from which the phosphoric acid is readily separated. However, in special circumstances it may be necessary to use hydrochloric acid ... 

Until other gibbereUins (- 80) can be either fermented or synthesized in bulk, their future is uncertain for use as industrial plant growth regulators except in very special circumstances. 

The distribution of the electric current lines leads to rounding of edges, thus very sharp corners caimot be produced by ECM. Tolerances of ca 0.127 mm are typical, although accuracies to 0.013 mm have been claimed under special circumstances. Reports on micro-ECM reveal that accuracy of ECM can be improved by special shielding and masking in order to direct the current flow only to required areas (6). 

Hydrogen produced by the electrolysis of water is used in special circumstances only where electric power is plentiful, inexpensive, and light hydrocarbons are not available. 

In the early 1970s, air pollution requirements led to the adoption of the double contact or double absorption process, which provides overall conversions of better than 99.7%. The double absorption process employs the principle of intermediate removal of the reaction product, ie, SO, to obtain favorable equiUbria and kinetics in later stages of the reaction. A few single absorption plants are stiU being built in some areas of the world, or where special circumstances exist, but most industriali2ed nations have emission standards that cannot be achieved without utili2ing double absorption or tad-gas scmbbers. A discussion of sulfuric acid plant air emissions, control measures, and emissions calculations can be found in Reference 98. 

Certain anaerobic bacteria capable of producing hydrogen may, under special circumstances, contribute to hydrogen embrittlement of some alloys. Once again, if such mechanisms operate, they have very limited applicability in most cooling water systems. 

This sample, referred to in Chapter 2, can serve as a guide for planning and conducting assessments of tollers. It may require additions, revisions, or other modifications in order to meet the needs of facility specific assessment objectives, the facility setting, or other special circumstances. This sample includes ... 

Figure 7.2 Three helical forms of DNA, each containing 22 nucleotide pairs, shown in both side and top views. The sugar-phosphate backbone is dark the paired nucleotide bases are light, (a) B-DNA, which is the most common form in cells, (b) A-DNA, which is obtained under dehydrated nonphysiological conditions. Notice the hole along the helical axis in this form, (c) Z-DNA, which can be formed by certain DNA sequences under special circumstances. (Courtesy of Richard Feldmann.)...

The last three detection schemes apply only under very special circumstances. Transmission EXAFS is strictly a probe of bulk structure, i.e., more than about a thousand monolayers. The electron- and ion-yield detection methods, which are used in reflection rather than transmission schemes, provide surface sensitivity, 1-1,000 A, and are inherendy insensitive to bulk structure. X-ray fluorescence EXAFS has the widest range of sensitivity—from monolayer to bulk levels. The combination of electron or ion yield and transmission EXAFS measurements can provide structural information about the X-ray absorbing element at the surface and in the bulk, respectively, of a sample. 

The existence of n-complex intermediates can be inferred from experiments in which they are trapped by nucleophiles under special circumstances. For example, treatment of the acid 1 with bromine gives the cyclohexadienyl lactone 2. This product results from capture of the n-complex by intramolecular nucleophilic attack by the carboxylate group ... 

If you cannot select suitable equipment for your current environment, you may need to control the environment in order to carry out the measurements. In such areas the environmental factors important to maintaining stable measurement should be monitored and the monitoring equipment calibrated. Chart recorders enable you to monitor conditions without having to be in constant attendance. The environment should be controlled in areas where calibration is carried out in order to provide stable conditions in which accurate and precise measurement can be taken. However, some modern equipment is so stable that environmental controls are unnecessary except in special circumstances. 

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