Effective growth rate, definition

Secondly, fractionation effects have been studied [126] where now the components are the various molecular weights in the solution. They conclude that fractionation will be important even at high molecular weights due to the variation in supercooling of the different molecular weights, and hence their different growth rates. Notice that this result could well be affected by the definition of supercooling as described in Sect. 2.3. 

This behavior is generally characterized by a plateau region, which prevails over a definite threshold It i usually referred to as stress CF as SCC systems usually exhibit this behavior, and the most common theory assumes that the crack growth rate is because of the addition of SCC and pure fatigue crack advance. This type of synergistic effect is observed in systems not sensitive to SCC such as ferritic stainless in seawater under cathode polarization. It is often associated with HE. It is possible that the plateau behavior is because of the control of crack growth rate by nonmechanical processes such as transport processes (73). 

It has been known for many years that an increase in molecular weight results in a decrease in growth rate for unfractionated polymers [12-15] however, definitive data is available for few commercially significant polymers. A thorough understanding of molecular weight effects requires a detailed evaluation of fractions. Few such smdies are available. 

Pines. Calorimetric studies of growth rates and temperature responses have not been employed to examine pine trees. Two studies were conducted to analyze effects of air pollutants on the respiration properties of Ponderosa and Jeffrey pine needles. Bower [104] used one-cm needle segments and demonstrated a correlation between the extent of ozone damage, measured as the number of lesions on the needles, and isothermal metabolic heat rates. He also measured increases in metabolic heat rates resulting from acid and nitrate deposition on the needles. Momen et al. [105] conducted a more controlled study of acid rain and ozone effects on Ponderosa pine with defined applications to plantation grown plants. In seedlings, metabolic heat rates increased in response to ozone and combinations of ozone and acid rain. Mature tree metabolic activities showed no response to ozone, acid, or combinations of the two. No studies were made to determine whether metabolic efficiencies were altered by these treatments. Thus the results show that calorimetry can be used to monitor pollutant effects on trees, but more definitive experiments must be done to identify how the ob.served responses relate to growth and survival of the trees. 

Discussion. The turbidity of a dilute barium sulphate suspension is difficult to reproduce it is therefore essential to adhere rigidly to the experimental procedure detailed below. The velocity of the precipitation, as well as the concentration of the reactants, must be controlled by adding (after all the other components are present) pure solid barium chloride of definite grain size. The rate of solution of the barium chloride controls the velocity of the reaction. Sodium chloride and hydrochloric acid are added before the precipitation in order to inhibit the growth of microcrystals of barium sulphate the optimum pH is maintained and minimises the effect of variable amounts of other electrolytes present in the sample upon the size of the suspended barium sulphate particles. A glycerol-ethanol solution helps to stabilise the turbidity. The reaction vessel is shaken gently in order to obtain a uniform particle size each vessel should be shaken at the same rate and the same number of times. The unknown must be treated exactly like the standard solution. The interval between the time of precipitation and measurement must be kept constant. 

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