Mechanical shuttling

The first method consists in mechanical translation of the sample between areas with different field intensities (15,16,50-64). However, such mechanical shuttling methods are inherently slow. It follows that they are applicable only to samples with long relaxation times, limited essentially by the shortest possible time it takes to move the sample from one position to another which is typically about 50 ms. 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

The mechanical equipment used in room-and-pikar underground mining usuaky involves a series of specific operations with continuous mining equipment. Continuous miners use rotating heads equipped with bits to pick or cut through the coal without blasting and load it into a shuttle car for conveying to a belt system. 

In oiological systems, the most frequent mechanism of oxidation is the remov of hydrogen, and conversely, the addition of hydrogen is the common method of reduc tion. Nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucleotide phosphate (NADP) are two coenzymes that assist in oxidation and reduction. These cofactors can shuttle between biochemical reac tions so that one drives another, or their oxidation can be coupled to the formation of ATP. However, stepwise release or consumption of energy requires driving forces and losses at each step such that overall efficiency suffers. 

Shuttle shifters that separate the plates one by one for cake discharge at a rate of 5-6 seconds per plate. A special design of the shifting mechanism ensures that two adjacent plates are not pulled together due to sticky cakes. 

The shuttle shifter moves the plates back one by one towards the fixed header. When each plate parks the cloth is washed at 100 bar with a mechanism that lowers and lifts a pair of symmetrical manifolds with high impact nozzles. 

Modern composite solid propellant is a mechanical mixture of the powder-like chemicals and a binding resin. The propellant used for the Space Shuttle solid rocket boosters (SRBs) is a typical example of such mixture ... 

Figure 7-6. Mechanism for catalysis by an aspartic protease such as HIV protease. Curved arrows Indicate directions of electron movement. Aspartate X acts as a base to activate a water molecule by abstracting a proton. The activated water molecule attacks the peptide bond, forming a transient tetrahedral Intermediate. Aspartate Y acts as an acid to facilitate breakdown of the tetrahedral intermediate and release of the split products by donating a proton to the newly formed amino group. Subsequent shuttling of the proton on Asp X to Asp Y restores the protease to its initial state.

In the rhizosphere, microorganisms utilize either organic acids or phytosiderophores to transport iron or produce their own low-molecular-weight metal chelators, called siderophores. There are a wide variety of siderophores in nature and some of them have now been identified and chemically purified (54). Pre.sently, three general mechanisms are recognized for utilization of these compounds by microorganisms. These include a shuttle mechanism in which chelators deliver iron to a reductase on the cell surface, direct uptake of metallated siderophores with destructive hydrolysis of the chelator inside the cell, and direct uptake followed by reductive removal of iron and resecretion of the chelator (for reviews, see Refs. 29 and 54). 

FIG. 25 (a) Schematic representation for a photocatalytic mechanism based on shuttle photosensitizers at liquid-liquid interfaces. (Reprinted with permission from Ref. 182. Cop5right 1999 American Chemical Society.) (b) This mechanism is compared to the photo-oxidation of 1-octanol by the heterodimer ZnTPPS-ZnTMPyP in the presence of the redox mediator ZnTPP. (From Ref. 185.)... 

Figure 7.22b shows that hydrophilic molecules, those with log Kj < 1, are much more permeable in octanol than in olive oil. The same may be said in comparison to 2% DOPC and dodecane. Octanol appears to enhance the permeability of hydrophilic molecules, compared to that of DOPC, dodecane, and olive oil. This is dramatically evident in Fig. 7.7, and is confirmed in Figs. 7.8c and 7.22b. The mechanism is not precisely known, but it is reasonable to suspect a shuttle service may be provided by the water clusters in octanol-based PAMPA (perhaps like an inverted micelle equivalent of endocytosis). Thus, it appears that charged molecules can be substantially permeable in the octanol PAMPA. However, do charged molecules permeate phospholipid bilayers to any appreciable extent We will return to this question later, and will cite evidence at least for a partial answer. 

Hammond TG et al. Mechanical culture conditions effect gene expression gravity-induced changes on the space shuttle. Physiol Genomics 2000 3 163-173. 

Long-chain fatty acids can slowly cross the mitochondrial membrane by themselves, but this is too slow to keep up with their metabolism. The carnitine shuttle provides a transport mechanism and allows control of (3 oxidation. Malonyl-CoA, a precursor for fatty acid synthesis, inhibits the carnitine shuttle and slows down (3 oxidation (Fig. 13-5). 

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