Closed-can method

Samuelsson, C., A Critical Assessment of Radon-222 Exhalation Measurements Using the Closed-Can Method, this volume (1987). 

At the time of the NBS review (Collfe et al., 1981) in 1981 no one had applied the results of time-dependent diffusion theory to the accumulation closed-can method. Therefore neither the review nor the earlier contemporary state-of-the-art papers (e.g. Jonassen, 1983) could describe properly or quantify the influence from radon... 

In order to experimentally check the validity of the time-dependent diffusion theory as applied to the closed-can method, extensive systematic investigations of radon exhalation, with carefully controlled parameters, are needed. To the author s knowledge no such investigations have yet been performed. 

Alternatively, one can use close-coupling methods. These methods are easiest to understand for single arrangement problems (i.e. when both the AB + C and AC + B product arrangements are very high in energy so that only the A + BC reactant arrangement can be accessed). Then one writes... 

The Ziegler and Nichols closed-loop method requires forcing the loop to cycle uniformly under proportional control. The natural period of the cycle—the proportional controller contributes no phase shift to alter it—is used to set the optimum integral and derivative time constants. The optimum proportional band is set relative to the undamped proportional band P , which produced the uniform oscillation. Table 8-4 lists the tuning rules for a lag-dominant process. A uniform cycle can also be forced using on/off control to cycle the manipulated variable between two limits. The period of the cycle will be close to if the cycle is symmetrical the peak-to-peak amphtude of the controlled variable divided by the difference between the output limits A, is a measure of process gain at that period and is therefore related to for the proportional cycle ... 

The efficiencies which may be obtained can consequently be calculated by simple stoichiometry from the equilibrium data. In the ease of countercurrent-packed columns, the solute can theoretically be completely extracted, but equilibrium is not always reached because of the poorer contact between the phases. The rate of solute transfer between phases governs the operation, and the analytical treatment of the performance of such equipment follows closely the methods employed for gas absorption. In the ease of two immiscible liquids, the equilibrium concentrations of a third component in each of the two phases are ordinarily related as follows ... 

A closely related method does not require conversion of enantiomers to diastereomers but relies on the fact that (in principle, at least) enantiomers have different NMR spectra in a chiral solvent, or when mixed with a chiral molecule (in which case transient diastereomeric species may form). In such cases, the peaks may be separated enough to permit the proportions of enantiomers to be determined from their intensities. Another variation, which gives better results in many cases, is to use an achiral solvent but with the addition of a chiral lanthanide shift reagent such as tris[3-trifiuoroacetyl-Lanthanide shift reagents have the property of spreading NMR peaks of compounds with which they can form coordination compounds, for examples, alcohols, carbonyl compounds, amines, and so on. Chiral lanthanide shift reagents shift the peaks of the two enantiomers of many such compounds to different extents. 

Cathodic reduction is the most promising approach to the removal of carbon dioxide from a closed atmosphere. Methods developed so far provide for electrode materials, electrolytes, and electrolysis conditions where CO2 can be reduced to hquid organic products of low molecular weight such as formic acid. More complex systems are required to regenerate foodstuffs from the rejects of human vital activities during... 

In a large survey of radon transport phenomena (Collfe et al., 1981) several exhalation measurement methodologies were reviewed. One of the laboratory techniques in that review, perhaps the most common one for exhalation measurements of small porous samples, will be scrutinized in this contribution. I am referring to the closed-can accumulation method, which means that the sample to be investigated is enclosed in a can and the exhalation of radon is determined from the radon growth in the air inside the can. 

Titration curve for seawater. The shape of the curve is dependent upon experimental conditions. The top curve is produced when seawater is titrated in an open container so that CO2 generated after incremental acid addition can escape into the atmosphere. The bottom curve is generated when seawater is titrated in a closed container. In this case, the pH drops faster during the initial part of the titration because of the build-up of CO2 as acid is added. Once the carbonate/carbonic acid equivalence point is reached, both curves converge upon the same pH for the same volume of acid added, but extensive laboratory work has demonstrated that better accuracy is achieved with the closed container method. Source From Pilson, M. E. Q. (1998). An Introduction to the Chemistry of the Sea. Prentice-Hall, p. 119. 

Knowledge of the molecular wavefunction enables us to determine the electron density at any given point in space. Here we inquire about the amount of electronic charge that can be associated in a meaningful way with each individual atom of a A -electron system. Our analysis covers Mulliken s celebrated population analysis [31], as well as a similar, closely related method. 

As for any ealibration method, we need a reliable set of standards where the atomie speetra have been measured and the eoneentration(s) of the analyte(s) is (are) known. Here reliable is used sensu stricto, whieh means that the standards should be as similar as possible to the unknown samples. This can be justified easily by recalling that ANNs extract knowledge from a training set to, later, predict unknowns. If and only if the standards resemble the unknowns closely can the ANNs be expected to extract the correct knowledge and predict future samples properly. As for MLR, PCR and PLS, this issue is of paramount importance. 

CC Closed Cup method for the measurement of the flash point. With this method, Sample vapors are not allowed to escape as they can with the open cup method. Because of this, flash points measured with the CC method are usually a few degrees lower than those measured with the OC. The choice between CC and OC is dependent on the (usually ASTM) standard method chosen for the test. 

The coordinate system used in the close-coupling method is the space-fixed frame. For simplicity we consider the atom-diatom scattering. The wave function iM(.R,r,R) for an atom-rigid rotor system corresponding to the total energy E, total angular momentum J, and its projection M on the space-fixed z axis can be written as an expansion,... 

In an analogous manner, the generation of alkyl radicals in benzene solution by the O-acyl oxime method results in the formation of alkylbenzenes with moderate to good yields for simple acids (equation 55). Use of pyridine as solvent leads to the formation of alkylpyridines as mixtures of ortho, meta and para isomers in which the para isomer predominates. The 0-acyI benzophenone oxime chemistry can also be applied to aryl acids in benzene or pyridine, resulting in the formation of mixed biaryls. A closely related method involves photolysis of mixed anhydrides of arenecarboxylic acids with the hydrox-amic acid A -hydroxy-Z-pyridone in benzene solution (equation 56). 

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