e presence of paramagnet nitroxide radicals. It is found that the relaxation effect of the paramagnets is enhanced 5-fold in H2@C60 compared to H2 under the same conditions. 13C relaxivity in C60 induced by nitroxide has also been measured. The resulting value of R1 for 13C is substantially smaller relative to the 1H relaxation in H2@C60 than expected solely on the basis of the smaller magnetic moment of 13C. The observed values of R1 have been analyzed quantitatively using an outer-sphere model for bimolecular spin relaxation to extract an encounter distance, d, as the dependent variable. The resulting values of d for H2 and (13)C60 are similar to the sum of the van der Waals radii for the radical and the corresponding molecule. The value of d for (1)H2@C60 is substantially smaller than the corresponding van der Waals estimates, corresponding to larger than expected values of R1. A possible explanation for the enhanced relaxivity is a contribution from hyperfine coupling. Based on the results reported here, it seems that not only is the hydrogen molecule in H2@C60 not insulated from magnetic contact with the outside world but also the interaction with paramagnets is even stronger than expected based on distance alone.

Arthroscopic reconstruction of the posterior cruciate ligament: a comparison of quadriceps tendon autograft and quadruple hamstring tendon graft.
Considerable controversies remain on the graft choice and fixation methods in the posterior cruciate ligament (PCL) reconstruction. The purpose of this study was to compare, at minimal 2-year follow-up, the outcomes of PCL reconstruction between using quadriceps tendon autograft and using quadruple hamstring tendon autograft. Case series. All patients received only PCL reconstruction without combined severe associated posterolateral instability. From 1996 to 1998, there were 24 patients who had a quadriceps tendon autograft, and 30 patients with hamstring tendon autograft. Twenty-two of the quadriceps tendon group and 27 of the hamstring tendon autograft