Criticality problems

E. R. Dyer, ed.. Critical Problems of Magnetospheric Physics, National Academy of Sciences, Washiagton, D.C., 1972. 

Scandium is very widely but thinly distributed and its only rich mineral is the rare thortveitite, Sc2Si20v (p. 348), found in Norway, but since scandium has only small-scale commercial use, and can be obtained as a byproduct in the extraction of other materials, this is not a critical problem. Yttrium and lanthanum are invariably associated with lanthanide elements, the former (Y) with the heavier or Yttrium group lanthanides in minerals such as xenotime, M "P04 and gadolinite, M M SijOio (M = Fe, Be), and the latter (La) with the lighter or cerium group lanthanides in minerals such as monazite, M P04 and bastnaesite, M C03F. This association of similar metals is a reflection of their ionic radii. While La is similar in size to the early lanthanides which immediately follow it in the periodic table, Y , because of the steady fall in ionic radius along the lanthanide series (p. 1234), is more akin to the later lanthanides. 

Deterioration of electrode performance due to corrosion of electrode components is a critical problem. The susceptibility of MHt electrodes to corrosion is essentially determined by two factors surface passivation due to the presence of surface oxides or hydroxides, and the molar volume of hydrogen, VH, in the hydride phase. As pointed out by Willems and Buschow [40], VH is important since it governs alloy expansion and contraction during the charge-discharge cycle. Large volume changes... 

Electrode corrosion is the critical problem associated with the use of metal hydride anodes in batteries. The extent of corrosion is essentially determined by two factors alloy expansion and contraction in the charge-discharge cycle, and chemical surface passivation by the formation of corrosion—resistant oxides or hydroxides. 

The primary question is the rate at which the mobile guest species can be added to, or deleted from, the host microstructure. In many situations the critical problem is the transport within a particular phase under the influence of gradients in chemical composition, rather than kinetic phenomena at the electrolyte/electrode interface. In this case, the governing parameter is the chemical diffusion coefficient of the mobile species, which relates to transport in a chemical concentration gradient. 

Major Suspension Reactor Problems. The critical problems in defining or optimizing a suspension reactor can be divided into three areas. In approximate order of importance, these are ... 

The use of statistically designed experiments in the development of both PS and RF foams has led to very significant progress, where critical problems were identified and solved quickly and where previously unexplored ranges of variables led to substantially improved materials. We shall continue to employ it in our development of low-density foams, and we strongly recommend it to other researchers. 

Wang et al. [96] constructed a Na/S battery with a sodium metal anode, liquid electrolyte, and a sulfur (dispersed in polyacrylonitrile) composite cathode and tested its electrochemical characteristics at room temperature. The charge/discharge curves indicated that sodium could reversibly react with the composite cathode at room temperature. Average charge and discharge voltage was 1.8 and 1.4 V, respectively. Similar to lithium batteries, dendrite formation was noted as a critical problem for these cells. 

The catalytic alcohol racemization with diruthenium catalyst 1 is based on the reversible transfer hydrogenation mechanism. Meanwhile, the problem of ketone formation in the DKR of secondary alcohols with 1 was identified due to the liberation of molecular hydrogen. Then, we envisioned a novel asymmetric reductive acetylation of ketones to circumvent the problem of ketone formation (Scheme 6). A key factor of this process was the selection of hydrogen donors compatible with the DKR conditions. 2,6-Dimethyl-4-heptanol, which cannot be acylated by lipases, was chosen as a proper hydrogen donor. Asymmetric reductive acetylation of ketones was also possible under 1 atm hydrogen in ethyl acetate, which acted as acyl donor and solvent. Ethanol formation from ethyl acetate did not cause critical problem, and various ketones were successfully transformed into the corresponding chiral acetates (Table 17). However, reaction time (96 h) was unsatisfactory. 

This book is about the scientific roots of our modern way of life. It tells the story of pioneering chemists like Berthollet whose discoveries solved critical problems in their lifetimes. Readers should be forewarned. The lives of these scientists tend to be dramatic. They are filled with the joys of discovery, the excitement of their times, and even the anguish of human tragedy. 

When the contaminated zone is located below the water table, the availability of oxygen becomes a critical problem due to the low solubility of oxygen in water. In adding the required oxygen, two kinds of systems are usually applied ... 

In summary, in order to address the critical problems of climate change and fossil fuel supply, we need greatly expanded sources of clean energy. It is dangerous to assume that nonnuclear sources will suffice. It is therefore important to strengthen the foundations... 

The main problem using planar methods is the difficulty in detection and collection of fractions among other less critical problems, such as homogeneous preparation of chromatographic media. However, the detection problem exists also for the coupled-column methods, mainly because of fraction dilution by each stage in a multidimensional separation system. Another aspect is the adjustment of chromatographic time bases between the different dimensions so that first-dimension peaks may be sampled an adequate number of times by the next dimension separation system. This aspect has been recently studied in detail (Murphy et al., 1998), and is covered in detail in Chapters 2 and 6. 

In addition to their use as stand-alone systems, LPs are often included within larger systems intended for decision support. In this role, the LP solver is usually hidden from the user, who sees only a set of critical problem input parameters and a set of suitably formatted solution reports. Many such systems are available for supply chain management—for example, planning raw material acquisitions and deliveries, production and inventories, and product distribution. In fact, the process industries—oil, chemicals, pharmaceuticals—have been among the earliest users. Almost every refinery in the developed world plans production using linear programming. 

Direct-methanol fuel cells (DMFCs) have attracted considerable attention for certain mobile and portable applications, because of their high specific energy density, low poison emissions, easy fuel handling, and miniaturization [129,130], However, the methanol permeation through electrolyte membranes (usually called methanol cross-over) in DMFCs still is one of the critical problems hindering the commercialization [131,132], Nafion , a... 

In Marshall Clagett, ed., Critical Problems in the History of Science, University of Wisconsin Press, Madison, 1959, pp. 519-24. 

On sociological constructivism, see Steven Shapin, "Discipline and Bounding The History and Sociology of Science as Seen through the External ism-Internal ism Debates," 203208, in Conference on Critical Problems and Research Frontiers in History of Science and History of Technology, 30 October 3 November (Madison History of Science Society, 1991). 

The compositions of biomass among fuel types are considerably varied, especially with respect to inorganic constituents important to the critical problems of fouling and slagging. Alkali and alkaline earth metals, in combination with other fuel elements such as silica and sulfur, and facilitated by the presence of chlorine, are responsible for many imdesirable reactions in combustion furnaces and power boilers. 

The second critical problem is the chemical instability of Li which deposits during the cycling of secondary cells. Electrodeposited Li has such a high surface area that it is not stable in many solutions in which flat Li foil is stable (45c). Howeyer, the pessimistic opinions of (45b and c) haye not inhibited the authors of (45a) from claiming a patent for a nonaqueous battery using chalcogenide electrodes, the specific structure of which is the main feature of the SB (46). 

Aluminum, a highly electropositive metal similar to the aUcaline earth metals, can be useful in deposition of low work function cathode metal electrodes in OLEDs and OELDs, and is preferred for many electronics applications because of its low cost and high conductivity, although it is somewhat prone to electro migration [8, 65]. Since A1 is an important metal for device applications its deposition on SAMs has been extensively studied [20, 21, 23, 32, 33,41, 50, 65-69]. The critical problem for Al, however, is its facility in penetration along with filament growth. 

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