Experimental restrictions

The shape of any rf pulse can be chosen in such a way that the excitation profile is a rectangular slice. In the light of experimental restrictions, which often require pulses as short as possible, the slice shape will never be perfect. For instance, the commonly used 900 pulse is still acceptable, while a 1800 pulse produces a good profile only if it is used as a refocusing pulse. Sometimes pulses of even smaller flip angles are used which provide a better slice selection (for a discussion of imaging with small flip angles, see Section 1.7). 

Although in principle a genetic algorithm, or other learning algorithm, shoutd f find the true optimum, the search is limited, either by computer limitations in th i case of numerical studies, or by experimental restrictions in the case of laboratory ir experiments. ij]... 

The reactor was considered being a ideal plug flow reactor when the rate constant for the HD formation was calculated. Because of experimental restrictions it was difficult to determine the HD formation rate when the H2-D2 reaction was close to equilibrium This will... 

The theoretical separation capabilities of Th-FFF have also been compared with those of capillary hydrodynamic fractionation (CHDF) [116]. Th-FFF was found theoretically to have the highest separation potential (also compared with SEC) and high selectivity which, however, is not fully accessible due to experimental restrictions. For CHDF, low selectivity but high efficiency as well as a very high analysis speed was predicted for samples with lower M but, experimentally, capillaries with very small tube diameters are not available in sufficient quality. In addition, such capillaries are very sensitive to clogging with minor amounts of impurities, e.g. dust. SEC was found to reach selectivities between Th-FFF and CHDF and had a high separation speed for lower molar masses M<105 g/mol. 

The fundamental strategy of computer-assisted library design is shown in Fig. 1. The set-up of the reaction scheme and building block selection lead to the virtual combinatorial library. Due to the virtual character of this library its size is not limited by experimental restrictions, and depends mainly on the number of available building blocks. 

There have been no studies measuring both carbon and nutrient fluxes in different morphological zones, nor studies relating net carbon sources and sinks to nutrient fluxes. For many reefs, errors in gross production and respiration are too high (10-15%) to get reliable estimates of net community production (Crossland etal, 1991) while changes in nutrient concentrations are nearly undetectable. Such experimental restrictions have limited our ability to understand the relationship between carbon and nutrient cycles in coral reefs. 

It was not possible to obtain a direct measurement of the solvent composition of the internal phase at equilibrium in these studies. A material balance needed to be effected by accurate analysis of the initial phases and the final equilibrium solution to yield this information. This experimental restriction blunted the accuracy and range of the experimental program as described below. 

To measure the equiUbrium potential of such a cell several experimental restrictions must be observed. Some examples are given in the following listing ... 

The discussion of the applications of DTA is divided into three parts. The first covers the more qualitative DTA, which was historically the first major DTA application. The term qualitative is chosen for these applications because no quantitative heat measurements are made. The temperature is, however, quantitatively fixed. Often transition temperatures can be fixed more precisely by such qualitative DTA than by the more quantitative DSC because of less stringent experimental restriction on sample mass and thermometer placement. Many of the thermometric measurements given in Chapter 3 can also be carried out by DTAand often with better results, so that Sect. 4.5 is an extension of the introduction to the thermodynamics of two-component systems given in Sect. 3.5. The measurement of heat is the... 

The analysis of distribution of the length of trains and loops has shown that it is very narrow, whereas for tails it is very broad. The , , and

values may be used to determine the length of the mean adsorbed chain , i.e., the chain with these characteristics. The theoretically calculated distribution functions include some parameters which cannot be found experimentally, restricting the possibilities of experimental verification. 

Abstract Theoretical chemical research in the area of the heaviest elements is extremely important. It deals with predictions of properties of exotic species and their behavior in sophisticated and expensive experiments with single atoms and permits the interpretation of experimental results. Spectacular developments in the relativistic quantum theory and computational algorithms have allowed for accurate calculations of electronic structures of the heaviest elements and their compounds. Due to the experimental restrictions in this area, the theoretical studies are often the only source of useful chemical information. The works on relativistic calculations and predictions of chemical properties of elements with Z > 104 are overviewed. Preference is given to those related to the experimental research. The increasingly important role of relativistic effects in this part of the Periodic Table is demonstrated. 

Isoleucine (lieu) occupies the positions 10. 17, and 55 from the amino-terminal end in the a-chain, and the position 112 of the /9-chain. The omission of lieu does not exert the same effect as the Try failure, because there is a sufiScient endogenous supply of the former amino acid. The use of the lieu antagonist. 0-methylthreonine, makes possible an experimental restriction of lieu for protein synthesis, since the analogue is activated by the transfer RNA . (In E, coli, however, the analogue may replace lieu for incorporation into protein.)... 

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