Shuttle-mode

Alternatively, two boluses can be used to acquire two slabs of CTP data at different levels, doubling the overall coverage [47], but -unlike shuttle-mode -requiring twice the contrast and potentially more than twice the radiation dose. Importantly, at least one... 

Coverage volume will continue to increase with enlarging detector arrays and improved technology. Cutting edge scanners with 320 detector rows offer the possibility of 16-cm coverage without the decreased temporal resolution required with shuttle-mode technique. However, some early clinical reports noted inferior image quality with 320-slice MDCT compared to 64-slice MDCT [83, 84]. 

In addition to the up-and-down or side motion methods, other modes of operations increase production. Three other popular modes of operation are the rotary wheel with its two modes (carousal system or fenis wheel) and a shuttle mode. The rotary-wheel method uses at least 2 to 20 clamping stations with the molds. These stations are mounted to a vertical or horizontal wheel. In one approach, the die with its parison moves around in the path of the molds. A mold is opened while the parison is moving through it. The mold closes, pinching the parison, and starts its cycle of blow, cool, and eject by opening the mold. In the meantime, the next mold is opened, and the parison is pinched and so on. This system is timed so that when the parison drop returns to the first mold, which is an open mold with part removed, the rotary system continues and repeats. The other rotary approach is having the molds move with the parison remaining in a fixed location. 

Fig. 1.18. Whole brain perfusion study on a Siemens SOMATOM Definition AS+ Using a detector configuration of 128x0.6mm and a detector coverage of 38.4mm, whole brain perfusion studies can be carried out by using a special spiral shuttle mode that uses a sinosoi-dal motion of the patient table to cover the whole brain for a period of 30 s...

Lower plate weight has reduced the downtime for shuttle shifting during the cake discharge mode. 

Mediated electrolyses make use of electron transfer mediators PjQ that shuttle electrons between electrodes and substrates S, avoiding adverse effects encountered with the direct heterogeneous reaction of substrates at electrode surfaces (Scheme 6). In recent years this mode of electrochemical synthesis has been widely studio and it is becoming increasingly well understood. A review is given in vol 1 of the present electrochemistry series... 

Phase transfer catalysis (PTC) refers to the transfer of ions or organic molecules between two liquid phases (usually water/organic) or a liquid and a solid phase using a catalyst as a transport shuttle. The most common system encountered is water/organic, hence the catalyst must have an appropriate hydrophilic/lipophilic balance to enable it to have compatibility with both phases. The most useful catalysts for these systems are quaternary ammonium salts. Commonly used catalysts for solid-liquid systems are crown ethers and poly glycol ethers. Starks (Figure 4.5) developed the mode of action of PTC in the 1970s. In its most simple... 

Liu et al. applied the SECM feedback mode to noninvasively probe the redox activity of individual mammalian cells [70,71]. In order to probe the redox activity of a mammalian cell, both oxidized and reduced forms of the redox mediator must be capable of crossing the cell membrane and shuttling the charge between the tip electrode and the intracellular redox centers (Fig. 23a). Only hydrophobic redox mediators (e.g., menadione and 1,2-naphthoquinone) could be used in SECM experiments with mammalian cells [71]. The redox reactions at the tip and inside the cell can be presented as follows ... 

To resolve the dilemma, one needs an additional analysis of the conduction mechanisms. For instance, the amount of electrons transported per period has been estimated on the basis of the known source-drain current I 100 pA [Park 2000]. However, when taking into account the frequency Q 1.2 THz of the "bouncing-ball mode", it turned out that the CV>o transistor transmits only a small fraction q 10-3 e of the elementary charge e per vibrational period r = 27t/Q 10 12 s. This excess charge is too small to compete with and to affect the shuttling dynamics of the Cm SET. 

Catalysts which contain reduced transition metal clusters besides acid sites are able to catalyze reactions that are not observed on catalysts exposing one type of site only. The reaction network is inadequately described by models which assume only additivity of catalytic functions and shuttling of intermediates between sites. There is strong evidence that metal clusters and Bronsted sites form metal-proton adducts. These act as "collapsed bifunctional sites" all alkane isomerization steps can take place on such sites during one single residence of the adsorbed molecule. At low temperature, adsorption in a mode reminiscent of a carbenium ion can suppress pure metal catalysis. 

This property is central to the mode of action of several enzymes which utilise the imidazole ring of a histidine. These include the digestive enzyme chymotrypsin, which brings about amide hydrolysis of peptides in the small intestine the enzyme provides a proton at one site, while it accepts a proton at another, making use of the ambivalent character of the imidazole ring to achieve this. The illustration shows how the heterocycle allows a proton to shuttle from one site to another via the heterocycle. 

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