Shedding Mechanisms

The cam system is most limiting in the complexity of weaves possible since only 8 to 10 harnesses can be effectively raised and lowered by this method. The cams are generally positioned below the harnesses and raise and lower the harnesses by use of mechanical tappets. For more complex weaves the dobby mechanism or the Jacquard system must be used. 

The dobby mechanian is actually mounted on the side of the loom and is capable of raising as many as 20 to 28 harnesses. The dobby mechanic uses a slotted dram and continuous pattern chain containing patterns of pegs on each bar of the pattern chain to lift selected harnesses during shedding. 

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The shedding mechanism is one of the primary motions of a loom. A Jacquard shedding mechanism is used for weaving 3D preforms because the individual warp fibers are controlled independently by Jacquard harness cords. A 3D fabric and preforms can be woven on a 2D conventional rapier loom, but there is a fabric thickness limitation when using any conventional 2D loom. 

A few companies have developed 3D looms (Mohamed et al., 1992/1995 3Tex Khokar, 2002 Uchida et al., 1999 Wilson et al., 1999). Mohamed et al. (1992/ 1995) and 3Tex have developed 3D looms. Figure 9.61 shows the filling insertion from both sides. The warp fibers are fed either from bobbins posititmed oti a creel or from beams. They are separated into layers to allow for fill insertion. These warp layers are fixed open to form sheds without the shedding mechanism. 

Studies on the mechanism of action of /3-lactam antibiotics have shed considerable light on how these agents kill bacteria. They also help explain qualitative differences between various agents and why there is a correlation between the reactivity of the /3-lactam and antibacterial activity. However, it is also clear that reactivity is only one factor in determining how effectively a given /3-lactam antibiotic will inactivate bacterial enzymes (82BJ(203)223). 

Flow measurements using nonintrusive or low mechanical ac tion principles are desired, such as magnetic, vortex-shedding, or Coriolis-type flowmeters. Orifice plates are easy to use and reliable but have a limited range and may not be suitable for streams which are not totally clean. Rotameters with glass tubes should not be used. 

In 1977 Fitton et al. conducted the first detailed study that shed light on the true mechanism of the Pictet-Gams reaction. It was postulated that all Pictet-Gams reactions create an oxazoline intermediate (15) by the mechanism shown below ... 

Some particles and fibers may be generated by indoor equipment (e.g. copy machines and printers). Mechanical abrasion and air motion may cause particle release from indoor materials. Particles are also produced by people, e.g., skin flakes are shed and droplet nuclei are generated from sneezing and coughing. Some particles may contain toxic chemicals. 

Kauffman [kauff86b] describes two related mechanisms respon.sible for the formation of such percolating walls (1) forcing structunrs and (2) internaJ homogeneity clusters. An important point to keep in mind is that these two mechanisms, described below, currently represent the only establi.shed means by which the ordered behavior of = 2 nets can (in part) be deduced. 

Nothing is known about the identity of the iron species responsible for dehydrogenation of the substrate. Iron-oxo species such as FeIV=0 or Fem-OOH are postulated as the oxidants in most heme or non-heme iron oxygenases. It has to be considered that any mechanistic model proposed must account not only for the observed stereochemistry but also for the lack of hydroxylation activity and its inability to convert the olefinic substrate. Furthermore, no HppE sequence homo-logue is to be found in protein databases. Further studies should shed more light on the mechanism with which this unique enzyme operates. 

Apart from the question whether the 14-electron species 12-B is a relevant intermediate, computational studies have been conducted in order to shed light on other aspects of the mechanism. Stereochemical issues, for instance, have not yet been investigated by experiment. DFT calculations suggest that attack of the alkene to 12-B occurs trans, because cis attack is associated with a rather high barrier [30b]. 

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