The choice of method

One of the problems facing the fabricator at this stage is that of making a logical choice of method inspection of the flow diagram in Fig. 2.7 shows how to make this choice. 

Increased assurance that the selected procedure is safe, but not so safe that it is unnecessarily expensive, can be gained only by carrying out tests to estimate the margin of safety. Ideally, these would be made on the fabrication itself, modifying the procedure in a series of tests to establish the point of maximum safety with minimum cost, but in most cases this would be an unacceptable exercise on economic grounds. It is recommended however that, whenever a high level of assurance is required, tests should be made to establish 

7 Sequence of decisions leading to final choice of welding diagram. 

In this case the HAZ will be hard and may have inadequate toughness and low resistance to stress-corrosion cracking. Postweld tempering could be employed but time at temperature should be restricted to minimise carbon migration at fusion boundaries. 

Proceed with isothermal transformation method select time and temperature see Ch4, pp. 66-67 

Pyridine base eliminations of a-bromo ketones cannot be recommended for general use because of the side reactions already discussed. The semi-carbazone-pyruvic acid method should be employed if strict absence of isomerization is required in the dehydrobromination of 2- or 4-bromo-3-ke-tones. This procedure is not applicable for the preparation of -3-ketones, 

Joly s method (or modifications) is the best procedure for preparing A -3-ketones and can be extended to the elimination of hydrogen bromide from a-bromo ketones of all types. Rearrangement is sometimes observed but is not often serious. Selectivity can be improved in some instances by lowering the reaction temperature. The method has been found useful for the preparation of A -3-ketones from 6-halo-A -3-ketones  

6-Dibromo-3-ketones may also be used as substrates for the preparation of A -3-ketones by Joly s method. Hexamethylphosphoramide has been recommended as a medium suitable for the dehydrobromination of a-bromo ketones to give a, -unsaturated ketones in high yield without rearrange- 

2a-Bromo-5a-cholestan-3-one (37) is dehydrobrominated by calcium carbonate in DMA. Other routes give purer product,but the method exemplified is simple and high yielding. The bromo ketone (37) may be obtained in pure form by chromatography of the product obtained from direct acid-catalyzed bromination of 5oc-cholestanone (36). ° Alternatively, (37) is available by buffered bromination of the enol-acetate of 5oc-cholestanone (39) ° which can be obtained from 5oc-cholestanone (36) in high yield.  

21-Acetoxy-17a-hydroxy-5a-pregnane-3,l 1,20-trione (40) is brominated in acetic acid under equilibrating conditions to give a solution of the 2a,4a-di-bromo compound (41). This is reduced by chromous chloride without further treatment, to the 4a-bromo compound (42). The recrystallized bromo compound (42) is then dehydrobrominated via the semicarbazone (43) which is converted without isolation into cortisone acetate (44) by treatment with pyruvic acid  

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The nature of the calculational bases, that is, the components and conditions of temperature and pressure, are too varied for it to be possible to make absolute recommendations as to the choice of methods. 

Attestation of the test procedure is realized with the aim to confirm both the correctness of the choice of method and NDT facilities and fullness of requirements included in the test procedure. Attestation ensures reliability of testing results with required accuracy. 

There is no one best method for describing solvent effects. The choice of method is dependent on the size of the molecule, type of solvent effects being examined, and required accuracy of results. Many of the continuum solvation methods predict solvation energy more accurately for neutral molecules than for ions. The following is a list of preferred methods, with those resulting in the highest accuracy and the least amount of computational effort appearing first ... 

Regardless of the choice of method, excited-state modeling usually requires a multistep process. The typical sequence of steps is ... 

Modeling the lighter main group inorganic compounds is similar to modeling organic compounds. Thus, the choice of method and basis set is nearly identical. The second-row compounds (i.e., sulfur) do have unfilled d orbitals, making it often necessary to use basis sets with d functions. 

Another way to narrow the choice of methods is to consider the scale on which the analysis must be conducted. Three limitations of particular importance are the amount of sample available for the analysis, the concentration of analyte in the sample, and the absolute amount of analyte needed to obtain a measurable signal. The first and second limitations define the scale of operations shown in Figure 3.6 the last limitation positions a method within the scale of operations. ... 

Potassium Chloride. The principal ore encountered in the U.S. and Canadian mines is sylvinite [12174-64-0] a mechanical mixture of KCl and NaCl. Three beneficiation methods used for producing fertilizer grades of KCl ate thermal dissolution, heavy media separation, and flotation (qv). The choice of method depends on factors such as grade and type of ore, local energy sources, amount of clay present, and local fuel and water availabiUty and costs. 

Because of the increa sing worldwide interest and demand for simple, effective, and inexpensive female sterilisation, a variety of procedures and methods have been developed. These approaches differ whether they are performed postpartum, postabortum, or in interval situations. The choice of methods also largely depends upon the physician s prior training, knowledge, and experience. Excellent reviews have been written on sterilisation (98). 

In this section, three methods for calculating the blast parameters of pressure vessel bursts and BLEVEs will be presented. All methods are related that is, one basic method and two variations are presented. The choice of method depends upon phase of the vessel s contents and distance to the blast wave s target, as illustrated in Figure 6.19. 

World production of HCl is of the order of 10 million tonnes pa, thus making it one of the largest volume chemicals to be manufactured. Four major processes account for the bulk of HCl produced, the choice of method invariably being dictated by the ready availability of the particular starting materials, the need for the co-products, or simply the availability of by-product HCl which can be recovered as part of an integrated process,... 

The choice of method from available resources depends largely upon the properties of the material to be analyzed, the basic significance or physical wearing of the measurement, and the purpose for which the information is required. For example, failure to disperse the particles as discrete entities is the biggest single problem in all size analysis methods that depend on individual particulate behavior. With microscopic techniques particles must be dispersed on the slide to permit observation of individual particles, and in sedimentation techniques the material must be suspended in the fluid so that the particles behave as individuals and not as floes. 

To summarize then, the choice of method should be dictated by the real needs of the submitter of the sample and not by the fanciness of the available instrumentation. 

The choice of method will depend on what information is available and how accurate and detailed the estimate mnst be. ... 

The choice of method used is often facilitated or constrained by the information available. In the absence of structural information on target, if one or more active small molecules are known, LBVS or PHBVS are feasible. If no active compounds are known, but an experimental or computational model of the protein structure is available, SBVS can be considered. If both active compounds and target structure are available, one or more appropriate methods can be applied, or multiple methods combined. 

The choice of method for a particular application should take into account this categorisation, as well as the precision and accuracy required. This chapter mainly deals with bulk analysis and speciation. 

Anodic hydroxylation/methoxylation of furans has an exact chemical counterpart in the well-known bromine/methanol reaction, and the choice of method is not always easily made. One can compare the two methods particularly easily in syntheses of the flavoring component, the pyrone maltol 121, from the furan 122 since one group used the electrolytic method299 and another the chemical method.300... 

There are a number of things to consider, but the most important is understanding the needs of the customer. Is the total sugar content of the product required or the lactose content The level of uncertainty in the result that is acceptable also helps focus on the choice of method. Once the method is chosen and validated, it is then important to ensure that all of the equipment is available and in a proper state of calibration. Then, all that remains is to have sufficient trained staff to carry out the analysis. Once the experimental results have been obtained and the data treatment is complete, the report can be written. The report also has to meet the customer requirements and should be written in an unambiguous way which is clear to the non-specialist. 

Hence, the choice of method and the validation of the method selected become increasingly more critical for those analyses resulting in actions towards the bottom of the list than for those at the top. You now need to pause to consider what the consequences of poor analytical work could be in your own particular job. Do not forget to include longer-term implications as well as the immediate problems. Poor or wrong data also result in the loss of reputation - customers who never come back. 

The choice of method depends on the purpose for which the analysis is being performed. The customer requesting the analysis may specify the method to be used. Even in this situation, it is the responsibility of the laboratory to demonstrate that the method is capable of producing results that are reliable. When no method is specified the points to consider have already been identified in Section 4.2. The acceptable level of measurement uncertainty specified or implied will, to a certain extent, set the precision and bias levels. All of the topics covered in the following sections may be crucial, depending on the purpose of the analysis, and should appear on your list. 

Ultimately, the choice of method will depend on several factors. Above all, fitness for purpose must be uppermost in your mind. Will the method you have selected be adequate for the decision you and/or your customer has to take when the result is available ... 

The major difference between this work and similar calculations by Krogh-Jespersen et al. (22) is the choice of method for the final energy calculations, B3LYP vs. BP86. We choose the latter because it appears to give better results for a similar well studied reaction. The principal difference for the mechanisms that arises from our choice is that the steps for reductive elimination have higher barriers, while those for oxidative additions have lower barriers. 

Once the structural support layers have been fabricated by extrusion or EPD for tubular cells or by tape casting or powder pressing for planar cells, the subsequent cell layers must be deposited to complete the cell. A wide variety of fabrication methods have been utilized for this purpose, with the choice of method or methods depending on the cell geometry (tubular or planar, and overall size) materials to be deposited and support layer material, both in terms of compatibility of the process with the layer to be deposited and with the previously deposited layers, and desired microstructure of the layer being deposited. In general, the methods can be classified into two very broad categories wet-ceramic techniques and direct-deposition techniques. 

The choice of method depends on the system to be investigated. The methods of intermolecular quenching and intermolecular excimer formation are not recommended for probing fluidity of microheterogeneous media because of possible perturbation of the translational diffusion process. The methods of intramolecular excimer formation and molecular rotors are convenient and rapid, but the time-resolved fluorescence polarization technique provides much more detailed information, including the order of an anisotropic medium. 

The various types of capillary electrophoresis are performed either in free solution or in gels. The choice of method depends on the nature of the sample and the analytical objective but capillary gel electrophoresis, including iso-electric focusing and SDS electrophoresis, is particularly useful for protein applications. 

Sangster, J. Lenzi,F., "On the Choice of Methods for the Predictions of the Water-activity and Activity Coefficients for Multicomponent Aqueous Solutions", Can. J. Chem. Eng.,... 

Fitness for purpose is the ultimate goal of the person doing the job in the laboratory, especially for the choice of method and instrumentation used to carry out an analysis. The validation of the analytical method is the important part to guarantee the fitness. 

Cost If the choice of method comes down to either Method A or Method B after having examined all facets of the work (detection limit, bias and accuracy, useful range, and capacity), the final decision may very well depend on cost. Cost includes all components of a budget (i.e., personnel, training, instrumentation, equipment, maintenance, supplies, overhead, and costs of using an outside laboratory for some or all of the work). All other factors being equal, if Method A is less expensive than Method B, then Method A should be chosen. 

A 2nd critical addition when planning a probabilistic assessment is the choice of methods for propagating variability and nncertainty. The workshop reviewed a range of contrasting methods of analyzing uncertainty in risk assessments ... 

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