Pulling speeds

The contribution that Hocking wished to make was to refine the sensor system and the instrumentation paekage so as to be able to incorporate the necessary functionality within a lightweight portable battery operated instrument. This implied a lower power level and very low-noise instrumentation. We aimed also for a low cost instrument able to operate for several hours from fully charged batteries and able to operate at a pull speed of 500mm/second. 

Our target is to detect a 2.5mm diameter OD pit, 40% through a 3mm wall of a 25mm diameter tube at a pull speed of 500mm per second... 

X 10 N and the value obtained by the simplest form, 1.45 X 10 " N m n = 918 and a = 0.31 nm for Equation 21.1). These comparisons imphed that the measurements were consistent with the theoretical predictions. The deviation between the rupture length of 260.9 nm and the fitted-contour length indicated that the polymer chain was not fully stretched at the rupture event. The reason for this was that the rupture event was a stochastic process and was dependent on many factors such as pulling speed, bond strength, and temperature. The vahdity of the freely jointed (FJC) model (dashed fine) was also checked ... 

FIGURE 21.6 Nanofishing with a very fast pulling speed (about 17 pm s for a single polystyrene chain in dimethyfibrmamide (DMF). A cantilever with a 30 pN nm spring constant was used. 

Figure 1-5. Free energy profile for the reaction from chorismate (RC 1.75) to prephenate (RC — 1.75), obtained using MSMD and Jarzynski s equality and pulling speeds of 2.0 A/ps (red) and 1.0 A/ps (green), and using umbrella sampling (blue)...

Fig. 8.3. Histogram of work values for Jarzynski s identity applied to the double-well potential, V(x) = x2(x — a)2 + x, with harmonic guide Vpun(x, t) = k(x — vt)2/2, pulled with velocity v. Using skewed momenta, we can alter the work distribution to include more low-work trajectories. Langevin dynamics on Vtot(x(t),t) = V(x(t)) + Upuii(x(t)yt) with JcbT = 1, k = 100, was run with step size At = 0.001, and friction constant 7 = 0.2 (in arbitrary units). We choose v = 4 and a = 4, so that the barrier height is many times feT and the pulling speed far from reversible. Trajectories were run for a duration t = 1000. Work histograms for 10,000 trajectories, for both equilibrium (Maxwell) initial momenta, with zero average and unit variance, and a skewed distribution with zero average and a variance of 16.0...

Figure 7. Mechanical unfolding of RNA molecules (a, b) and proteins (c, d) using optical tweezers, (a) Experimental setup in RNA pulling experiments, (b) Pulling cycles in the homologous hairpin and force rip distributions during the unfolding and refolding at three pulling speeds. (C) Equivalent setup in proteins, (d) Force extension curve when pulUng the protein RNAseH. Panel (b) is from Ref. 86. Panels (a) and (d) are a courtesy from C. Cecconi [84]. (See color insert.)...

Forward and Reverse Work Distributions Cross at W = AG. In order to obtain AG we can measure the forward and reverse work distributions, Pp(W) and Pr(—W), and look at the work value W where they cross, P-p W ) =Rr(—W ). According to Eq. (41), both distributions should cross at W = AG independently of how far the system is driven out of equilibrium (i.e., independently of the pulling speed). Figure 9 shows experiments on a short canonical RNA hairpin CD4 (i.e., just containing Watson-Crick complementary base pairs) at three different pulling speeds, which agree very well with the FT prediction. 

To prevent cracking and excessive, exotherm-induced residual stresses in thick composites, as well as to allow increased pulling speed, preheating may be used to heat either the... 

The characteristics of the three most common thermoset resin systems used in pultrusion are compiled in Table 11.2 [3]. It is noteworthy that unreinforced polyesters and vinylesters shrink 7-9% upon crosslinking, whereas epoxies shrink much less and tend to adhere to the die. These epoxy characteristics translate into processing difficulties, reduced processing speed, and inferior component surface finish. It is normal practice to use resin additives to improve processability, mechanical properties, electrical properties, shrinkage, environmental resistance, temperature tolerance, fire tolerance, color, cost, and volatile evaporation. It is normally the resin, or rather its reactivity, that determines the pulling speed. Typical pulling speeds for polyesters tend to be on the order of 10-20 mm/s, whereas speeds may exceed lOOmm/s under certain circumstances. Apart from the resins characterized in Table 11.2, several other thermosets, such as phenolics, acrylics, and polyurethanes, have been tried, as have several thermoplastics (as will be discussed in Sec. 11.2.6). 

Figure 11.3 Example of a system that exhibits stick-slip friction. Stick-slip is also illustrated as a schematic plot of spring elongation versus time at constant pulling speed v.

As to fibers, it was reported that the inferior mechanical properties of silk from cocoons compared to spider silk result from the silkworm spinning process. If silkworm silk is processed at a constant pulling speed rather than constant force pulling, it possesses excellent properties, approaching the spider dragline silk (Shao and Vollrath, 2002). This suggests that the silkworm silk has the potential to produce better fibers, and the regenerated fibroin, which is easy to harvest, has the possibility to be fabricated into a reconstituted super-fiber. 

VL = Velocity of the line (pulling speed) VM = Velocity of melt exiting die... 

Figure 35.6 shows pictures of the inner tube coating reactor. The reactor is a dual-vacuum system. The top of a sample tube is connected to the monomer feed-in system and the bottom is connected to a pumping system, which constitutes one vacuum system. The majority of the tube is rolled on a spool in the bottom section (not shown). The outside of the tube (within a quartz tube) is pumped by another pump system. The monomer flows from top to bottom, and the tube is pulled from bottom to top. In this counterflow mode, the deposition occurs on the uncoated portion of the tube. The coating thickness is controlled by the WjFM and the pulling speed, which is controlled by a surface speed control device, of the tube that determines the resident time of a section of surface in the glow. 

One trivial solution may be taken asU = —(j) —av) = constant independent of space and time coordinate. Here, all the blocks are moving uniformly at the pulling speed relative to the rough surface. However, such a solution can be shown to be unstable against small fluctuations. Considering small perturbations of wavelength q, one can study the stability of the solution... 

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