Some Theoretical Considerations

In this section, we will briefly consider two useful theoretical aspects in studying the radiation chemistry of gases. 

Water is essential for the rehydration of seeds as the initial step towards germination. The amount of water taken up by an imbibing seed depends upon a number of factors (e.g. size, hydratability of contents, etc.) but in absolute terms it is quite small and often may not exceed 2-3 times the dry weight of the seed. For establishment and subsequent growth of the seedling, a larger and sustained water supply is required. 

Two major factors have to be considered when discussing water uptake by a seed. These are (1) the water relations of the seed and (2) the relationship between the seed and its substrate, which in nature is of course the soil. In order to understand the water relations of a seed cell we must first consider the concept of water potential. Water potential ( f/) is an expression of the energy status of water. Net diffusion of water occurs down an energy gradient from high to low potential. The water potential in the cell (ij/ cell) can be formulated thus  

This means that ij/ cell is affected by 3 factors (1) this is the osmotic or solute concentration effect. The concentration of dissolved solutes in a cell will influence water uptake, the greater the concentration, the greater the attractive force to water (2) the matric (or hydrational) potential is contributed by the ability of matrices (e.g. cell walls protein bodies) to be hydrated and bind water (3) the turgor (hydrostatic) pressure occurs because as water enters a cell the contents swell and exert a force upon each unit area of the cell wall. Turgor pressure is in fact the amount by which pressure inside the cell exceeds the atmospheric pressure outside. 

The forces with which water is held in the soil, and the amount of work 

Thus the difference in water potential between seed and soil (ij/e— s) is only one of the factors on which the rate of flow of water from the environment to the seed depends. Initially upon imbibition the difference in water potential between the seed and soil is enormous, but as seed moisture content increases the water potential of the seed increases (becomes less negative) and that of the surrounding soil decreases as water is withdrawn. Since the seed cannot move towards the source of moisture, successful germination depends on the movement of sufficient moisture to the seed surface. This in turn depends on the water potential of the zones of soil immediately surrounding the seed and on the rate at which water moves through the soil, i.e. the hydraulic conductivity of the soil (the reciprocal of I l—the soil impedance). Impedance is important in soils which are in the process of drying, especially if they are coarsely textured, and in comparison the impedance to water flow exhibited by many seed coats ((2) is very small. Another factor which is important is the area of contact between soil particles and the seed surface—the reciprocal of this value is the external impedance (7). 

At the next pages a hypotheticel neural representation of reaaion tasks is proposed. 

We have, therefore, two parallel effects of reducing the layer5 neurons the cycle time between the two layers is prolonged and the searching set does not fit to the task elements as exactly as usually. This implies inappropriate elements in the searching set. 

Such a situation has many consequences the search covers inappropriate elements and omits appropriate elements.The slowing down of searching sets is only the beginning. If the loss of layer5 cells continues, the emergence of inappropriate searching sets becomes possible. 

If one excludes the possibility of guess or accidentally pressing the key, but takes these short times as real reaction times then they would give us the minimal possible pathways of this task. Therefore the minimal visual reaction time would be  

The underlined times can be summed up as the non-cortical time. This would mean a minimal visual reaction time of 170 ms. If there are lower times, the pathway either has some shortcuts or it does not use the cortex at all but passes only subcortical areas. 

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During the development of a chemical process, a choice must be made regarding the type of reactor to be used on a plant scale. Some theoretical considerations and their practical impact on reactor issues are presented here. Choosing the right type of reactor can indeed improve the safety of the process. The considerations are reflected as well in the mode of operation. Reactors are characterized by type of operation (i.e., batch, semi-batch, and continuous). 

Werlen, R.C. Effect of Resolution on the Shape of Mass Spectra of Proteins Some Theoretical Considerations. Rapid Commun. Mass Spectrom. 1994, 8, 976-980. 

Colin, H. and Guiochon, G, Comparison of some packings for reversed phase high performance hquid sohd chromatography, ii. Some theoretical considerations, J. Chromatogr., 158, 183, 1978. 

Lawrence, S. (1972). Some theoretical considerations of fiber pull-out from an elastic matrix. J. Mater. Sci. 7, 1-6. 

In Chapter 1 the validity of a stress-optical law has been presumed. Furthermore, it has been shown for several polymer systems that this law is, at least approximately, valid and that the second normal stress difference (p22 — p33) must be very small compared with the first normal stress difference (pn — 22). In the present chapter some theoretical considerations of a more general character will be reviewed in order to indicate reasons for this special behaviour of flowing polymer systems. Some additional experimental results will be given. 

Some theoretical considerations about vibrational band intensities. Spectrochim. Acta 14, 161—180 (1959). 

F. A. Williams, A Review of Some Theoretical Considerations of Turbulent Flame Structure, in AGARD Conference Proceedings No. 164, Analytical and Numerical Methods for Investigation of Flow Fields with Chemical Reactions, Especially Related to Combustion, M. Barrere, ed., AGARD, NATO, Paris (1975), II 11 to II 1-25. 

Eriksson E. (1965) Deuterium and oxygen-18 in deuterium and other natural waters some theoretical considerations. Tellus 16, 498-512. 

A.P. Bruins, B.F.H. Drenth, Experiments with the combination of a micro-LC and a Cl quadrupole MS, using a capillary interface for DLL Some theoretical considerations concerning the evaporation of liquids from capillaries into vacuum, J. Chromatogr., 271 (1983)71. 

In the discussions above and in the examples previously described, it has been assumed that the variables to be included in the multivariate regression equation were known in advance. Either some theoretical considerations determine the variables or, as in many spectroscopic examples, visual inspection of the data provides an intuitive feel for the greater relevance of some variables compared with others. In such cases, serious problems associated with the selection of appropriate variables may not arise. The situation is not so simple where no sound theory exists and variable selection is not obvious. Then some formal procedure for choosing which variables to include in a regression analysis is important and the task may be far from trivial. 

This ansatz can be rationalized by some theoretical considerations [325,326]. It is also supported by the experimental data at very low concentrations of the component A where the study is reduced to the dynamics of the probe A in host B. Each probe molecule experiences the same environment, which eliminates the complications from concentration fluctuations. We have mentioned in Section III, paragraph 4, that the probe rotational correlation function indeed has the Kohlrausch form. The differential between the probe rotational time xA and the host a-relaxation time xaB is gauged by their ratio, xA/xaB. As expected, the slower the host B compared with the probe A, the larger the coupling parameter, nA = (1 — pA), obtained from the stretch exponent (3A of the measured probe correlation function. The experimental data are shown in Fig. 52. For more details, see Ref. 172. 

Box 4. Is the Earth Sufficiently Old to Originate Life (after Fenchel et al, 1998) There are some theoretical considerations on the period of life s origin on the Earth based on the requirement of a definite time period for protein molecule evolution. 

We have defined the solvation process as the process of transfer from a fixed position in an ideal gas phase to a fixed position in a liquid phase. We have seen that if we can neglect the effect of the solvent on the internal partition function of the solvaton s, the Gibbs or the Helmholtz energy of solvation is equal to the coupling work of the solvaton to the solvent (the latter may be a mixture of any number of component, including any concentration of the solute s). In actual calculations, or in some theoretical considerations, it is often convenient to carry out the coupling work in steps. The specific steps chosen to carry out the coupling work depend on the way we choose to write the solute-solvent interaction. 

Moreover, when rate constants are measured or derived somehow from experimental data, one can assume that the expression for the rate constant in the Arrhenius form can be used as an approximation, even if the meanings of Z and //a are different from those followed from Eqs. (3.3) or (3.4). However, the situation is substantially different when we evaluate or calculate rate constants basing on some theoretical considerations. The discussion about applicability of such simple equations to reactions in condensed phase and/or interfaces has repeatedly ignited and extinguished during the last few decades. To our opinion, nowadays, when various theoretical methods are widely used for evaluation and calculation of rate constants, it is time to revert to the question. 

F. Peters and C. Marrase. Effects of turbulence on plankton an overview of experimental evidence and some theoretical considerations. Mar. Ecol. Prog. Ser., 205 291-306, 2000. 

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