Pinching forces

Voluntary closing devices require an opening force to be overcome before the terminal device will close (default to open position). Pinch force in a voluntary closing terminal device is directly proportional to the force qyplied to the device through the control cable. 

As the synchroniser can monitor the rotation of the hand wheel, it can also count the number of rotations of the hand wheel. One complete rotation of the hand wheel equates to one stitch formation. To ensure that thread is not slipped out of the needle hole while starting the next sewing cycle, all generations of computerised machines have one thread catcher and thread wiper fitted near the needle point. While the thread wiper swipes away the thread tail towards the right side of the stitch line, the thread catcher holds the thread end by suction or pinch force to ensure that the thread is not shpped out of the needle hole while starting the next sewing cycle. 

The interest in vesicles as models for cell biomembranes has led to much work on the interactions within and between lipid layers. The primary contributions to vesicle stability and curvature include those familiar to us already, the electrostatic interactions between charged head groups (Chapter V) and the van der Waals interaction between layers (Chapter VI). An additional force due to thermal fluctuations in membranes produces a steric repulsion between membranes known as the Helfrich or undulation interaction. This force has been quantified by Sackmann and co-workers using reflection interference contrast microscopy to monitor vesicles weakly adhering to a solid substrate [78]. Membrane fluctuation forces may influence the interactions between proteins embedded in them [79]. Finally, in balance with these forces, bending elasticity helps determine shape transitions [80], interactions between inclusions [81], aggregation of membrane junctions [82], and unbinding of pinched membranes [83]. Specific interactions between membrane embedded receptors add an additional complication to biomembrane behavior. These have been stud-... 

Partial Pressure Pinch An example of the hmitations of the partial pressure pinch is the dehumidification of air by membrane. While O9 is the fast gas in air separation, in this apphcation H9O is faster still. Special dehydration membranes exhibit a = 20,000. As gas passes down the membrane, the pai-dal pressure of H9O drops rapidly in the feed. Since the H9O in the permeate is diluted only by the O9 and N9 permeating simultaneously, p oo rises rapidly in the permeate. Soon there is no driving force. The commercial solution is to take some of the diy air product and introduce it into the permeate side as a countercurrent sweep gas, to dilute the permeate and lower the H9O partial pressure. It is in effect the introduction of a leak into the membrane, but it is a controlled leak and it is introduced at the optimum position. 

Figure 19.6 Nonisothermal mixing degrades temperature driving forces and might transfer heat across the pinch.

At one end of the scale are those individuals who lack all sensitivity to the usual pain stimulibums, cuts, bruises, etc. Such a person was a boy at Johns Hopkins who could have pins thrust into him his skin could be pinched until it became bloodshot his Achilles tendon could be squeezed with full force without any indication of discomfort. He did have a normal sense of touch and was sensible to cold and heat throughout his body surface, but nowhere was there a response to pain. 

When a drop (water) falls to a flat interface (benzene-water) the entire drop does not always join the pool (water). Sometimes a small droplet is left behind and the entire process, called partial coalescence, is repeated. This can happen several times in succession. High-speed motion pictures, taken at about 2000 frames per second, have revealed the details of the action (W3). The film (benzene) ruptures at the critical film thickness and the hole expands rapidly. Surface and gravitational forces then tend to drag the drop into the main pool (water). But the inertia of the high column of incompressible liquid above the drop tends to resist this pull. The result is a horizontal contraction of the drop into a pillar of liquid above the interface. Further pull will cause the column to be pinched through, leaving a small droplet behind. Charles and Mason (C2) have observed that two pinches and two droplets occurred in a few cases. The entire series of events required about 0.20 sec. for aniline drops at an aniline-water interface (C2, W3). 

After the preparation of ethylmagnesium bromide is completed, the separatory funnel is replaced by a bent tube which reaches the bottom of the flask and is bent at the outer end for downward delivery (Note 3). The warm (40-50°) solution is forced under nitrogen pressure (by carefully pinching off the tube to the mercury bubbler) into the 500-ml. separatory funnel which has been prepared for attachment to the 1-1. (lask. Afler all the... 

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