Phantom fibril

Fig. 24. a Schematic view of the craze tip showing a molecule about to be drawn into two different fibrils, b Phantom fibril of undeformed polymers, diameter Dq, is ultimately drawn into a fibril of diameter D = The entangled chains in the isotropic network, represented... 

One can estimate the fraction of the original network chains that remain unbroken after fibrillation. Consider, for example, the cylinder of imdeformed polymer of diameter Do shown in Fig. 24b. After fibril formation this phantom fibril cylinder is drawn into a fibril of diameter D = The entangled chains in the... 

Oq total number of entangled strands in the phantom fibril from which the... 

One can estimate the strand survival fraction q theoretically. The relevant parameters are the strand end-to-end distance d and the phmtom fibril diameter D, the diameter of starting polymer glass that is drawn into the final fibril, determined from smaU-angle electron (or X-ray) scattering. One can show that q is only a function of the ratio, Dg/d. The best method of calculation treats the strand as a Gaussian coil, with rms end-to-end distance d, and computes the probability that if one places one end at random in a cylindrical phantom fibril, the other end will be also inside For typical D s for polystyrene crazes (of the order of 14-20 nm at room temperature) the predicted values of q lie between 0.5 and 0.6, in satisfactory agreement with the experimental estimates (which include effects of the tie-fibrils not included in the theoretical method ° ). 

From the microscopic picture for the craze growth it seems clear that one important microscopic variable must be the mean number n of entangled strands within each fibril which survive the geometrically necessary strand loss associated with the interface formation. If the number of such strands is zero, the fibril will fail, since the polymer fluid which flows from the active zone into the fibril has no strain hardening capability and will not be able to support the relatively high tensile stresses necessary to propagate the interface. To obtain n one first estimates n, the total number of strands in the undeformed phantom fibril from which a craze fibril is drawn and which is given by ... 

Inappropriate therapy is the most common adverse event associated with ICDs (53). With the first generation of ICDs (Ventak 1500,1550, inappropriate shocks ranged from 15-25%. Unfortunately, the frequency of inappropriate therapy with the latest generation of devices is probably similar (5). In the Defibrillators in Nonischemic Cardiomyopathy Treatment Evaluation (DEFINITE) Trial, that evaluated the use of ICDs in patients with nonischemic cardiomyopathy, inappropriate therapy was more likely than appropriate therapy (22 versus 18%) (78). A case of an inappropriate shock due to noise oversensing inducing ventricular fibrillation and subsequent death in a patient has been reported (79). Finally it is important to confirm from the device that therapies were in fact delivered phantom shocks are not uncommon, occurring in approximately 6-7% of people (80). 

---