Extensional Step Strain Rate Experiments on an Entangled Polymer Solution

The dynamics of chain entanglement/disentanglement in concentrated polymer solutions are matters of current debate. We report the results of step strain rate experiments in uniaxial extensional flow on a well-characterized polymer solution containing about 22 entanglements per chain which allows these dynamics to be probed. In these experiments the polymer solution is subjected to homogeneous stretching at a given strain rate up until a predetermined value of strain. After this strain is reached, the strain rate is changed to a new value, and stretching is continued until steady state is acquired in the extensional stress. The strain rates are increased in step-up experiments and decreased in step-down experiments. The strain rates are adjusted so that both the orientation and the stretching dynamics can be probed. Additionally, the predictions of two recent single-mode molecular models are evaluated against the experimental data. These models include the effects of entanglement dynamics in their predictions in an ad hoc manner. This leads to only a qualitative improvement in the predictive capacity of one of the models and reduces that of the other. Slip-link simulations using the primitive chain network model are also included for further insight into the underlying dynamics. The models are found to yield qualitative predictions of the experimental observations

Concomitant (without adjuvant) temozolomide and radiation to treat glioblastoma: A retrospective study.

Between November 2004 and August 2006 we treated 35 patients with concomitant temozolomide (TMZ) and radiotherapy. Twelve patients had very large or multi-centric glioblastoma multiforme (GBM) with a poor performance status and received TMZ plus radiation doses of 45 to 50.4 Gy. Median survival of these patients was only 3.8 months and any benefit from treatment was small. Twenty three patients would have been eligible for randomisation in the EORTC/NCIC trial comparing combined and adjuvant TMZ plus radiation against radiotherapy alone. This group of patients received 60 Gy in 30 fractions plus comitant TMZ (75mg/m2) but no adjuvant chemotherapy. At a median follow-up of 26 months, 5 out of 23 patients are alive. The median survival time was 17 months (1.43 years 95% CI 0.96 to 1.55 years). 18% were alive at 2 years. Toxicity from temozolomide was infrequent. This series adds to indirect evidence that the concomitant rather than the adjuvant is the most efficacious part of the EORTC/NCIC schedule for this type of patient. Further trials should include a concomitant chemoradiotherapy regimen as well as a concomitant plus adjuvant chemotherapy