Tread-milling

Two examples where actin polymerization is observed in eukaryotes are in the bacterial pathogens Listeria monocytogenes and Shigella flexneri. The motion that the eukaryote pathogens exhibit is the actin based motility in the cytoplasm of their host. Actin polymerization is known to occur via an insertion polymerization mechanism. The movement is a result of site-directed tread-milling of the actin filaments. This type of movement is classified as a propulsive type motion. The driving force for actin pol)unerization as well as the next motor is the conversion of adenosine triphosphate (ATP) to adenosine diphosphate (ADP). ... 

Microtubules exhibit two dynamic phenomena that are pronounced at tubulin concentrations near the Q (1) tread-milling, the addition of subunits at one end and their loss at the other end, and (2) dynamic instability, the oscillation between lengthening and shortening (see Figure 20-9). 

Figure 3 The monomers having ATP (T) or ADP (D) near two ends of F-actin during polymerization of G-actin having ATP tread-milling may happen.

In the case of polymerization of G-ATP-actin, the ratio of the rates of association and dissociation of monomers is different at two ends. The critical concentration of G-ATP-actin is defined by the condition that the sum of the growth rates at the two ends and the sum of the depolymerization rates are equal. At one of the two ends, the depolymerization may be faster than the growth and at the other end, the growth may be faster. Then a cycling of actin monomers takes place from one end of F-actin to the free monomer to the other end. This phenomenon was named tread-milling [27]. As a result, the polymer translates. Consumption of the free energy of ATP hydrolysis is required for such unidirectional translation of F-actin. The coupling of the polymerization with an irreversible chemical reaction produces a dynamic function of the polymer. 

In cooperation with many kinds of actin-binding proteins, the G-F transformation of actin generates translational movement of a bacterial cell in a host cell, as in Figure 10 [46], Anchoring and nucleation proteins, depolymerizing proteins, and cross-linking proteins work to make possible a fast cycle of actin molecules from one end of F-actin to the other end, that is, tread-milling. This system has been artificially reconstructed in vitro [47]. 

The avadabihty of prompt iadustrial scrap is directiy related to the level of iadustrial activity. Producers geaeraHy do aot accumulate prompt iadustrial scrap because of storage requiremeats and iaventory control costs. Thus, it is rapidly available to the scrap consumer or the ferrous scrap iadustry. Prompt iadustrial scrap comes from imported steel as well as domestic steel mill products. Obsolete scrap, also known as old or post-coasumer scrap, is widely used. Treads ia aew steelmaking capacity and the reduced proportions of premium scrap iadicate that use of obsolete scrap should be expected to iacrease. 

Bead, tread, tube formation Washdown, spills, leaks Oil and solvent-based cements from the cementing operation oil from seals in roller mills... 

Rubbers are also being extruded, in a not essentially different way from plastics. Cooling of the extrusion cylinder is necessary to prevent premature vulcanisation as a result of the heat developed by internal friction. The extruder is fed by ribbons, obtained from milled sheets. End products are hoses, profiles, and cable mantles. On-line vulcanisation can be achieved by passing the extrudate through a steam channel, while the rate of extrusion is adjusted to the rate of curing. For this purpose high-rate vulcanisation recipes have been developed. Steam temperatures of about 200 °C are being applied (15 bars pressure). Treads for motorcar tyres are also extruded they are wrapped round the pre-formed carcass and then formed and vulcanised in a press. 

Another popular kind of grinding machines are tool grinders (Fig. 3). Those machines are used for production or resharpening of drills, mills, tread cutters, inserts, etc. To fulfill these operations, CNC tool grinders have at least five full CNC-controlled axes (here three translational and two rotational axes). 

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