Trade-off relationships

The objective weights quantify the trade-off relationship between the sub-objectives. They can be obtained with any of the above-mentioned methods, but commonly a direct estimation is used with these simple methods. The combination of the simple scoring method with the ratio or swing weights approach is also referred to as Simple Multi-Attribute Rating Technique or SMART (cf. Goodwin and Wright 2004, pp. 27-58 von Winterfeldt and Edwards 1986, pp. 259-287). 

Figure 8.3 Oxygen/nitrogen selectivity as a function of oxygen permeability. The upper-bound line represents the point above which no better membranes are known [12]. This line shows the trade-off relationship between membrane permeability and selectivity.

When considering toxicity manifestation time and vapor dispersion, the detection sensitivity for vapor concentration is one hundredth of LCtso within 1 min. In the case of GB, this required detection sensitivity is 0.15 mg/m, and at this level there is no odor and humans show no signs of toxicity. In the chemical weapon disposal situation, because the workers stay in one place for a long time, the time weighted average (TWA) values are the monitoring target for allowed operational conditions. These TWA values are approximately 1/100,000 of LCtso. The desired alarm time is to be less than several minutes. There is a trade-off relationship between LOD, alarm time, detection accuracy and... 

Robeson [4] showed that there exists a trade-off relationship between selectivity and permeability for dense polymer membranes. This plot was later updated by Singh and Koros [9] (see Figure 4.1). Molecular transport of light gases in such membranes typically occurs by a solution diffusion mechanism (as discussed in Section 4.2.1). For a polymer membrane to be commercially considered for the removal of CO2 from H2, CH4, or air, both the CO2 permeability and selectivity must be competitively high. Since the gases in the mixture with CO2 often are smaller (H2) or about the same size as CO2, they may diffuse more rapidly through the polymers, and it follows that the diffusion selectivity will be <1. The only way... 

However conventional positive electron beam resists like PMMA(4) or PBS(5.) do not have excellent dry etching resistance. The electron beam sensitivities of these positive resists primarily result from radiation-induced degradation of polymer main chains. If the main chain bonding force of these polymers is weakened in order to improve sensitivities, the dry etching resistances of these polymers will decrease. In such cases, sensitivity to electron beam exposure and dry etching resistance are in a trade-off relationship. 

The same relationship between plant complexity and loss in raw material value to fuel also exists in petrochemical processing. The three common raw materials for ethylene manufacture in the U.S.—ethane/propane, naphtha, and gas oil—exhibit similar trade-off relationships between processing complexity and fuel value loss (see Table I). 

Most of the research work has been focused on polymer membrane materials involving a solution-diffusion mechanism. The performances of such materials generally fall within the trade-off relationship between permeability and selectivity suggested by Robeson [5], with an upper bound limit for the membrane performances. 

ME is consistent with the slow convergence of transportation and other energy systems. The studies into ME considered household market segments, and found that only about 4 million out of 34 million California residents would most likely be able to adopt ME-enabled FCVs. There does appear to be a trade-off relationship between ME-power and driving range, as well as similar give-and-take situations within the supply framework. However, as questions arise over BEVs, market forces may well be opening the door for ME innovation in the FCV sector (Williams and Kurani, 2006,2007). 

There is no doubt that the perfluorinated ionomer membranes take initiative in this field and contribute a great deal in the commercialization and wide diffusion of fuel cells in the early stage. In terms of environmental compatibility (recyclability or disposability) and production cost, the perfluorinated ionomer membranes should be replaced with non-fluorinated alternative materials within the next decade. Challenge is how to achieve comparable conductivity and durability with the non-fluorinated membranes. Currently, no alternative materials have overcome the trade-off relationship between these two conflicting properties. In addition to the... 

As for solid acids, it should be noted that there are already very green processes using acid catalysts in solution (not solid) as exemplified later. It is also noted in these examples that the greermess very much depends on the selectivity of the reaction and the separation of products and catalysts. Therefore, we must consider carefully for each case the trade-off relationships between risk and benefit and between one risk and other risks. Several methods at different levels may be necessary for the evaluation. For ordinary chemists and chemical engineers involved in R D, an easily applicable method is desirable. 

Guiver et al. of National Research Council, Canada developed comb-shaped poly(arylene ether) electrolytes containing 2-A sulfonic acid groups on aromatic side chains (d) [76]. Their membranes showed relatively high proton conductivity and well-developed and continuous ionic domains. However, trade-off relationship between water uptake and proton conductivity of their membranes was not better than that of Nafion. In order to pronounce the hydrophilic/hydropho-bic differences, another series of comb-shaped aromatic ionomers with highly fluorinated main chains and flexible poly(a-methyl styrene sulfonic acid) side chains were developed [77]. The membranes seemed to have better properties than their previous version, however, chemical instability of the side chains needed to be improved. 

Battery separators are characterized by numerous properties, including material nature, membrane stractural and functional properties. Material nature includes chemical stability, crystalline structure, hydrophilicity, thermal shrinkage, melting point, M and Mv,/M of polyolefin materials. Structural properties include thickness, porosity, pore size, pore shape, pore tortuosity, and pore distribution. Functional properties include mechanical strength, electrical resistivity, air permeability, thermal shutdown, electrolyte wettability and retention. Many of the above properties are affected with each other and may be in a trade-off relationship. For example, the mechanical strength is affected in opposite manner by the thickness, porosity and permeability, as required by the battery performance. 

Understanding trade-off relationships lies at the heart of a focal firm s ability to achieve competitive advantage. Relationships that need to be imderstood and harnessed include recognising that ... 

The tolan liquid crystal drastically surpassed the other cmiventional liquid crystals having large An at that time such as a pyrinudine liquid crystal (An = 0.196, viscosity at 20 °C = 37.7 mPa s) or a biphenyl liquid crystal (An = 0.195, viscosity at 20 °C = 52.8 mPa s) in characteristics. By the synergy effect of the tolan and the alkenyl, the breakthrough of the trade-off relationship between the response and the contrast was achieved [70]. The STN-LCD, of which response time was improved from about 300 to 120 ms, was applied to a note PC, and the market was expanding. Now the liquid crystals including the liquid crystaUine tolan are used widely in about 80 % of total liquid crystals for STN-LCD. 

Table 2.2 Comparison among perovskite cathodes (LSM, LSF, LSC) in their trade-off relationship between chemical stability and performance with emphasis on the reaction with YSZ and Cr vapors [21]...

Doped ceria and doped lanthanum chromites were investigated a long time ago because ceria is a mixed conductor in a reducing atmosphere, whereas lanthanum chromites are typical candidates for oxide interconnects. Neither of the materials shows good performance as an anode. In recent years, other types of perovskite oxides have attracted attention, as is described in other chapters of this book. The basic trade-off relationship associated with oxide anodes is stability versus performance. 

---