Alkaline cell characteristics

Phosphorothioates generally protect normal tissues more than tumors. Tumor protection reported in some animal studies can pardy be explained by physiological effects of the particular dmgs, which are specific to rodents (4). WR-2721 does not appear to protect human and most animal tumors, apparentiy because of the low availabiUty of the dmg to tumor cells (4). Many tumors appear to have a reduced capillary density (44), which may mean that these tumors have altered levels of alkaline phosphatase, the enzyme that converts WR-2721 to WR-1065. A reduced abiUty of thiols to protect the hypoxic cells characteristic of many tumors may also contribute to their selectivity for normal tissues. The observation that WR-1065 protects cultured normal human fibroblasts, but not fibrosarcoma tumor cells, suggests that additional factors may contribute to the selectivity of radioprotection by WR-2721 m vivo (18). 

The manufacture of secondary batteries based on aqueous electrolytes forms a major part of the world electrochemical industry. Of this sector, the lead-acid system (and in particular SLI power sources), as described in the last chapter, is by far the most important component, but secondary alkaline cells form a significant and distinct commercial market. They are more expensive, but are particularly suited for consumer products which have relatively low capacity requirements. They are also used where good low temperature characteristics, robustness and low maintenance are important, such as in aircraft applications. Until recently the secondary alkaline industry has been dominated by the cadmium-nickel oxide ( nickel-cadmium ) cell, but two new systems are making major inroads, and may eventually displace the cadmium-nickel oxide cell - at least in the sealed cell market. These are the so-called nickel-metal hydride cell and the rechargeable zinc-manganese dioxide cell. There are also a group of important but more specialized alkaline cell systems which are in use or are under further development for traction, submarine and other applications. 

Alkaline Primary Cells, Fig. 8 Capacity loss on storage of various miniature alkaline cell systems compared to carbon-zinc and lithium-manganese dioxide cells. The lithium-based cells have significantly better storage characteristics compared to alkaline and carbon-zinc cells... 

Alkaline Primary Cells, Fig. 11 Discharge characteristics of the zinc-air alkaline cell at various temperatures. The performance falls off quickly below 20 °C, due to buildup of the peroxide reaction intermediate (Courtesy of Duracell)... 

The lithium-copper oxide battery has two special characteristics. Its initial voltage is approximately 2 V, but when fully loaded it drops to a flat 1.5 V. Thus it can be used as a direct replacement for carbon and alkaline cells. (Most other lithium batteries have voltages from 2.8 to 3.5 V.) Lithium-copper oxide also has a wide temperature range, spanning —55 to -H25°C. Although it is not the highest performance lithium combination, its voltage and temperature characteristics permit applications in specific niches. 

It should be noted that not all the BPM can be useful in this hybrid acid-alkaline cell. The particular BPM chosen for this acid-alkaline hybrid cell should possess the following characteristics (1) adequate durability, mechanical strength, chemical stability, and resistance to strong bases and acids (2) high perm-selectivity in the concentrated electrolyte (3) low electrical resistance and (4) thermal stability of the functional groups and structure of the membrane during thermal expansion and increased swelling. 

FIGURE 2.16 pH versus enzymatic activity. The activity of enzymes is very sensitive to pH. The pH optimum of an enzyme is one of its most important characteristics. Pepsin is a protein-digesting enzyme active in the gastric fluid. Trypsin is also a proteolytic enzyme, but it acts in the more alkaline milieu of the small intestine. Lysozyme digests the cell walls of bacteria it is found in tears. 

Amalgamated zinc powder has been used as the negative material to prevent zinc corrosion and zinc passivation. Recently, from the viewpoint of environmental problems, mercury-free alkaline-manganese batteries were developed by using zinc powder with indium, bismuth and other additives [2-4]. Adding indium to zinc powder is the most effective way to improve the characteristics of the cells [3]. Figure 3 shows the variation in the internal impedance of the cells according to the additive content of the zinc powder. 

Figure 4. Comparison between the discharge characteristics of newly developed and conventional alkaline-manganese cells (load 7.5 Q temperature 20 °C)...

Perhaps the first practical application of carbonaceous materials in batteries was demonstrated in 1868 by Georges Le-clanche in cells that bear his name [20]. Coarsely ground MnO, was mixed with an equal volume of retort carbon to form the positive electrode. Carbonaceous powdered materials such as acetylene black and graphite are commonly used to enhance the conductivity of electrodes in alkaline batteries. The particle morphology plays a significant role, particularly when carbon blacks are used in batteries as an electrode additive to enhance the electronic conductivity. One of the most common carbon blacks which is used as an additive to enhance the electronic conductivity of electrodes that contain metal oxides is acetylene black. A detailed discussion on the desirable properties of acetylene black in Leclanche cells is provided by Bregazzi [21], A suitable carbon for this application should have characteristics that include (i) low resistivity in the presence of the electrolyte and active electrode material, (ii) absorption and retention of a significant... 

Freshly isolated or subcultured brain microvascular endothelial cells offer a notable in vitro tool to study drug transport across the blood-brain barrier. Cells can be grown to monolayers on culture plates or permeable membrane supports. The cells retain the major characteristics of brain endothelial cells in vivo, such as the morphology, specific biochemical markers of the blood-brain barrier, and the intercellular tight junctional network. Examples of these markers are y-glutamyl transpeptidase, alkaline phosphatase, von-Willebrandt factor-related antigen, and ZO-1 tight junctional protein. The methods of... 

A significant cost advantage of alkaline fuel cells is that both anode and cathode reactions can be effectively catalyzed with nonprecious, relatively inexpensive metals. To date, most low cost catalyst development work has been directed towards Raney nickel powders for anodes and silver-based powders for cathodes. The essential characteristics of the catalyst structure are high electronic conductivity and stability (mechanical, chemical, and electrochemical). 

Although several fuel cell technologies are reaching technical maturity, the economics of a fuel cell are not clear. The commercial potential of fuel cells will depend on the ability to reduce catalyst and other expensive materials costs and to manufacture the units at a competitive cost. Many uses of fuel cells place a premium on specific performance characteristics. The relatively simple alkaline fuel cells (AFC)... 

Fig. 4.24 Capacity of lithium-copper oxide button cells (LC 01) as a function of discharge current (solid lines). Dashed lines indicate the characteristics of alkaline manganese cells of similar dimensions. (By courtesy of SAFT Gipclec.)...

Progress was made possible by use of a different source for membrane preparations. It had been shown by Felix and Boiler [26] that cell suspension cultures of a wild tomato species (Lycopersicon peruvianum) give a characteristic response to systemin. After addition of systemin an alkalinization of the culture medium was observed paralleled by an efflux of K+. Systemin also caused an increase in the activities of 1-... 

Epithelial cells of small intestine were prepared in a fractional way (4), the older, less adherent villus tip cells being washed out by EDTA-containing phosphate buffer first, while mitotic crypt cells appeared in the final fractions. The enzyme characteristics of the series of fractions obtained (Fig. 13) followed conventional criteria for differentiated (villus) and less differentiated (crypt) cells (3, 4). The thymidine kinase activity decreased from crypt to villus while the activity of alkaline phosphatase increased (Fig. 13). 

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