Orientation Correlation in Simplified Models of Polymer Melts

We investigate mutual local chain order in systems of fully flexible polymer melts in a simple generic bead-spring model. The excluded-volume interaction together with the connectivity leads to local ordering effects which are independent of chain length between 25 and 700 monomers, i.e. in the Rouse as well as in the reptation regime. These ordering phenomena extend to a distance of about 3 to 4 monomer sizes and decay to zero afterwards.Comment: 5 pages, 3 figure

Deriving effective mesoscale potentials from atomistic simulations

We demonstrate how an iterative method for potential inversion from distribution functions developed for simple liquid systems can be generalized to polymer systems. It uses the differences in the potentials of mean force between the distribution functions generated from a guessed potential and the true (simulated) distribution functions to improve the effective potential successively. The optimization algorithm is very powerful: convergence is reached for every trial function in few iterations. As an extensive test case we coarse-grained an atomistic all-atom model of poly (isoprene) (PI) using a 13:1 reduction of the degrees of freedom. This procedure was performed for PI solutions as well as for a PI melt. Comparisons of the obtained force fields are drawn. They prove that it is not possible to use a single force field for different concentration regimes.Comment: 32 pages including 12 figure

Anterior short correction in thoracic adolescent idiopathic scoliosis with mini-open thoracotomy approach: prospective clinical, radiological and pulmonary function results

Introduction: This is a prospective study of adolescent patients in whom idiopathic thoracic scoliosis was corrected by short anterior fusion through a mini-open thoracotomy approach. Clinical, radiological and pulmonary function results of minimal 2-year (2-6) follow-up are presented. Materials and methods: Consecutive 62 patients with Lenke 1 and 2 curves, having main thoracic scoliosis of up to 75°, were prospectively included. The shoulder imbalance in Lenke 2 patients was less than 20mm. Thoracic scoliosis was corrected by short anterior fusion. The thoracic spine was exposed by an 8-cm mini-open thoracotomy incision. The operation technique and choosing of fusion levels are thoroughly described. Complete 360° discectomies and convex side vertebral endplates osteotomies are essential for deformity corrections with short fusions. Single-rod 5.5-mm titanium implants were used. The age at the time of operation was mean 15.2 years; 56 patients had a single thoracic curve and 6 patients had a double thoracic curve. There were almost equal numbers of patients with lumbar modifier A, B or C. The average length of fusion was 5.5 (4-7) vertebrae. The average length of fusion was 3.5 (2-6) vertebrae shorter than the average curve length. Results: The instrumented thoracic curves improved by 58.3% at 6 weeks and 56.3% at the last follow-up. Apex thoracic vertebral rotation improved by 73.78% at 6 weeks and 76.24% at the last follow-up. The non-instrumented upper thoracic curve improved by 25% in double thoracic scoliosis, where the mid-thoracic curve was selectively fused, and the non-instrumented lumbar curves improved by 33.9% at the last follow-up. The radiological changes from 6 weeks to the last follow-up were statistically not significant. The clinical rib hump improved by 54% at the last follow-up. There were no significant changes in the pulmonary function. FVC% was 81.04% preoperatively, 76.41% at 6 months and 80.38% at the 2-year follow-up. The results of SRS 24 questionnaire improved from a total of 61.40 points preoperatively to 100.50 points at 6 months and 98.62 points at the 2-year follow-up. There were no neurological or thoracotomy related complications, no pseudarthrosis, no implant pullout or breakage. Conclusion: A good deformity correction without loss of correction or adding on, a good cosmetic result and good patient's satisfaction were achieved through shorter than end-to-end thoracic fusions. The radiological residual deformity is acceptable. Anterior correction of thoracic scoliosis with a short spinal fusion is recommended to keep the large part of the spine mobile. A very short fusion, small thoracotomy incision, low-profile implants and complete closure of parietal pleura are keys to prevent reduction in postoperative lung functio