Fractionation effect

Applications While any metal can be evaporated irrespective of its physical form, the method is restricted chiefly by the capacity of the vacuum plant and by the economic time available for the required thickness. Alloys such as Al-Cu, Sn-Cu and Ni-Cr, which do not fractionate unduly can also be deposited, while other alloys showing a greater tendency to fractionate may be dealt with by rapid evaporation, which minimises the fractionating effect. 

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. 

Figure 1 Is a flow sheet showing some significant aspects of the Iterative analysis. The first step In the program Is to Input data for about 50 physical, chemical and kinetic properties of the reactants. Each loop of this analysis Is conducted at a specified solution temperature T K. Some of the variables computed In each loop are the monomer conversion, polymer concentration, monomer and polymer volume fractions, effective polymer molecular weight, cumulative number average molecular weight, cumulative weight average molecular weight, solution viscosity, polymerization rate, ratio of polymerization rates between the current and previous steps, the total pressure and the partial pressures of the monomer, the solvent, and the nitrogen.

Without isotope dilution, the simultaneous measurement of U and Th is essential in LA-MC-ICPMS, although large (10-100% level) elemental, matrix-dependent fractionation effects can still be observed between U and Th (e g., Stirling et al. 2000). As a result, Th/U ratios can be systematically lower, and apparent U- Th-ages... 

In this way, it is possible to reach an extremely high selective sensitivity down to 1 part in 1015, which in 14C dating corresponds to being able to date samples about 50 000 years old. Moreover, modern systems can measure isotopic ratios in modern carbon, both C/ C and C/ C, with an ultimate precision as good as 2%o and l%o, respectively. The former value corresponds to determining the conventional radiocarbon age with an absolute error, smaller than in the past, better than 20 years, while the l%o precision for the 13C/12C allows an adequate correction for isotopic fractionation effects. Even in routine measurements, at least in the case of historical samples, a precision of 5%o in the 14C/12C measured value is standard, corresponding to an uncertainty in the radiocarbon age of 40 years.[27]... 

Table II. Summation of Fractional Effective (Lethal) Doses for 30-Minute Exposure of Rats to Mixtures of CO and HQ...

Hartzell, G.E. Emmons, H.W. "The Fractional Effective Dose Model for Assessment of Hazards Due to Smoke from Materials," J. Fire Sciences 1988, 6(5), 356-362. 

The Fractional Effective Dose (FED) of toxicant received by an exposed person is defined by Hartzell (5.6) as... 

Figure 10. The percent probability of incapacitation or death as dependent on the corresponding Fractional Effective Dose (FED) defined by Equation 1.

It is clear from figure 6 that the terrestrial data do not cluster about a single point but instead lie along a line of slope 0.5 on the three-isotope diagram, indicating isotopic variation due to mass-dependent fractionation. Since mass fractionation effects in Mg have not been observed in terrestrial materials [30,31], this distribution of observed isotope ratios must be due to fractionation in the ion probe. The physical process which produces the... 

A comparison of uniform and pore mouth poisoning appears in P7.06.08 as a function of fractional poisoning. At a given fraction, effectiveness is reduced much more by pore mouth poisoning. 

In contrast, Meckenstock et al. [280] reported larger isotopic enrichments in residual toluene, 3-6%o and up to 10%o during anaerobic and aerobic biodegradation experiments, respectively. These results indicated that isotopic fractionation effects may be different for different compounds, terminal electron-accepting processes (TEAP), degradative metabolic pathways, or microbial populations. 

Equations (8) and (10) are applicable to stable isotope systems where isotopic fractionation occurs through mass-dependent processes which comprise the majority of cases described in this volume. These relations may also be used to identify mass-independent fractionation processes, as discussed in Chapter 2 (Birck 2004). Mass-dependent fractionation laws other than those given above distinguish equilibrium from kinetic fractionation effects, and these are discussed in detail in Chapters 3 and 6 (Schauble 2004 Yormg and Galy 2004). Note that distinction between different mass-dependent fractionation laws will generally require very... 

The nucleosynthetic sources for Ti isotopes are very similar to those of the isotopes of Ca, and Ti requires a neutron-rich zone to be produced in significant amoimts. In addition to the nonlinear effects, absolute isotopic compositions have been measured in a number of samples using double spike techniques (Niederer et al. 1985). Mass dependent fractionation effects are rarely resolved and are small, below 1 %o/amu except in one sample, where it reaches 1.3 %o/amu. In general the fractionation is in favor of the heavy isotopes partial condensation or evaporation may explain of this observation. 

Figure 10. On this unusually fractionated block of 40 cycles, the effect of the noise-induced correlation observed on Zn isotopes can be separated from the mass fractionation effects. The solid line corresponds to mass-dependent fractionation, while the dashed line is defined by counting statistics. When the larger Zn/ "Zn and Zn/ "Zn ratios are plotted against each other (top), counting statistics tend to pull the results away from the mass fractionation line. When the smaller "Zn/"Zn is considered (bottom), counting statistics has essentially no effect. Data acquired using the VG Plasma 54 of Lyon.

A correlation between isotopic ratios corrected for mass fractionation may reveal (i) rormded or slopping peak tops (ii) second-order fractionation effects. The necessity of a second-order correction should be established by showing that the bias left after a first-order correction still depends smoothly on the mass. 

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