DUAL HARDNESS

Microbial resistance to established organic antibiotics is a potentially serious problem and provides an impetus for the development of novel antimicrobial metal compounds. The potency of Ag(I) ions is well known—but how does Ag(I) kill a bacterium Much current attention is focused on Bi(III) on account of its ability to kill Helicobacter pylori, an organism which prevents ulcers from healing. Bis-muth(III) chemistry has many unusual features a variable coordination number, strong bonds to alkoxide ligands, the stereochemical role of its 6s2 lone pair, facile formation of polymers, and dual hard and soft character. 

Dual hardness armor plate armor-soft steel and armor-aluminum ... 

Dual-Hardness Molded Foam A number of formulations for molded foams have been reported. A new development in recent years is dual-hardness molded foams. Automotive seats and furniture have been labor-intensive products. These products provide good comfort by using different layers of different hardnesses. Molded foams produced by using a single formulation have relatively comfortable cushioning properties in terms of sag factor. However, this advantage is not enough to satisfy customers requirements for comfort. 

Recent trends are the increased use of MDI-based flexible foams because higher density foams with good comfort are obtained. Also, dual hardness foam cushioning can be produced more easily with MDI systems. Hot cure TDI foams are being phased out. In Table 12 the distribution of the systems used in the global automotive seating production are shown. 

Traditionally, solid seat pans were regarded as inferior to frames with lattice springing. Improvements in polyurethane technology such as dual hardness foams have transformed the situation. Once the solid seat pan became acceptable, it was inevitable that steel should be replaced by one or other plastic material. The asymmetrical rear seat of the 1989 Peugeot 405 estate car features two pans in injection moulded glass-reinforced PP, with a variety of textile covering options (see Fig. 4.10). Other versions have followed on this theme, notably in PP-GMT. 

The 1989 Ford Fiesta was the first example of a unit seat in a volume car. The dual hardness foam was moulded directly in the textile eover, lined with a barrier film, with the fixtures already positioned for assembly within the ABS shell (see Fig. 4.11). The 1990 BMW 3-series featured bucket seats made in PP-GMT, in a process which included automated finishing and inline painting, all within a one-minute cycle. These seats however still use steel for the safety-critical parts of the structure the seat back and the seat sub-frame. In fact, new seat designs in production still owe more to develop-... 

For automotive seat cushions, two different PUR mixtures are poured into the open moid, either simultaneously or one shortly after the other, to create foams of different hardness to produce the so-called dual-hardness seat cushion . For comfort reasons, the sides of the seats are stiffer than in the center. At the beginning of filling the mold, the joining of the two reaction mixtures of very low viscosity is prevented by separation walls that create grooves between the sides and the center (Figure 1.114). These grooves are later required for fixing e.g. the textile seat cover. 

FIGURE 1.114 Principle of mold for dual-hardness seat cushion ... 

Selenium is a vital microelement for people. It has dual properties. Selenium is an essential nutrient at low concentration levels and it becomes toxic at higher concentration levels. Deficiency of selenium results in weakness and hard diseases. Selenium is a building material of many hormones and ferments it neutralizes free radicals, radioactive radicals in organism. The range of selenium safety concentration in food and water is very narrow. The daily normal amount of human consumption of selenium is 10-20 p.g, maximum safe concentration of selenium in water is 5-10 p.g/1. It becomes toxic at 20-30 p.g and bigger content in different objects. 

Hammett equation(s) 78, 93, 148ff., 151 f., 153ff., 167f., 190, 193, 196, 297, 299, 308, 312, 375, 381, 392, see also Dual substituent parameter, and Quantitative structure-reactivity relationships Hammond postulate, in additions of nucleophiles to diazonium ions 157 Hard and soft acids/bases principle (Pearson) 49, 54, 109... 

No decomposihon into atom contribuhon is possible, because X not only occurs as the solute, but also as the solvent in (xl. In other words, since the drug is in a dual role of solute and solvent, it is not possible to dissect the contribuhon of individual atoms or groups of atoms in the drug from their role in the solvent state from that in the solute. Reiterahng this important point, log carmot be assumed to be accessible by linear regression with respect to composition descriptors, as is the case for log P . Moreover, it can hardly be - as often assumed - a linear function of log Pow, because the latter is linear with respect to composihon. Thus, any account of log S requires the nonlinear character to be taken into account. 

Experiments were conducted with a dual catalyst chain shuttling system in a continuous solution polymerization reactor. A series of ethylene-octene copolymers of similar melt index were produced with a composition of ca. 30% (by weight) hard and 70% soft blocks. The level of DEZ was systematically varied to study the effects of CSA ratio on polymer microstructure. 

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. 

It is important to mention that the chemical potential and the hardness, p, and 17, are global-type response functions that characterize the molecule as a whole, while the electronic density p(r), the Fukui function fir), and the dual descriptor A/(r) are local-type response functions whose values depend upon the position within the molecule. 

The use of a dual descriptor defined in terms of the variation of hardness with respect to the external potential, and it is written as the difference between nucleophilic and electrophilic Fukui functions, Equation 12.21, can also be used as an alternative to rationalize the site reactivity [32] ... 

The combination of the dual electrophilic character of DMC with its reaction products allows two consecutive steps to occur in a selective way for what concerns both reaction sequence and yields first, the hard-hard reaction occurs and produces a soft anion only and second, a soft-soft nucleophilic displacement leads to the final product. Since hard-soft and soft-hard interactions are inhibited, double methylation and double carboxymethylation do not occur. 

Betamethasone is hardly ever used orally. It has a long duration of activity and can therefore also be used for alternate-day therapy. The parenteral formulation is also the sodium phosphate salt which when given IV or IM has a rapid onset of action. There are many similarities with dexamethasone such as their metabolic pathways and the indications for which both steroids are used, like the prevention of neonatal RDS and reduction of raised intracranial pressure. Combinations of betamethasone acetate and sodium phosphate have, when used for intra-articular and intra-lesional injections, the dual advantage of a rapid onset of action together with the long duration of action of a depot preparation. 

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